Analysis of 3D Strain in the Human Medial Meniscus and Comparison to 3D Strain in Meniscal Allograft Transplants
By Sandra Kolaczek
A Thesis presented to The University of Guelph
In partial fulfilment of requirements for the degree of Master of Applied Science in Engineering
Guelph, Ontario, Canada © Sandra Kolaczek, 2015 ii
ABSTRACT
Analysis of 3D Strain in the Human Medial Meniscus and Comparison to 3D
Strain in Meniscal Allograft Transplants
Sandra Kolaczek Advisors: University of Guelph, 2015 Dr. Karen Gordon Dr. Mark Hurtig
A method of measuring 3D strain in-vitro is presented. Regional 3D meniscal strain has not been studied in a large number of human knees under simulated physiological loading. Strain is calculated by tracking markers implanted within the meniscal tissue using computed tomography imaging under simulated physiologically relevant loading. No statistically significant difference between strain in the middle or posterior of the meniscus or between the principal directions of strain is uncovered.
Strain in meniscal allograft transplants (MAT) is also evaluated with two surgical fixation techniques; both use soft tissue anterior and posterior root fixation via transosseous suture but one also includes a third peripheral transosseous suture fixation. No significant difference was found. These results suggest that postoperative MAT perform in a similar manner to the native meniscus, and the addition of a peripheral anchor may not be necessary to replicate native tissue strain or improve the chondroprotective effect.
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Acknowledgements
I would like to sincerely thank and acknowledge everyone who provided support to this research. I would first like to thank my advisors Karen Gordon and Mark Hurtig for their vast patience, knowledge, support and direction. I would also like to thank Alan Getgood who performed the surgeries and provided guidance for this research.
I would also like to thank my fellow students who participated in the long testing days; Mikael Ragbar,
Chris Hewison, Scott Catarine and Trevor Beveridge. Their help in specimen preparation and dissection to coordination of testing was indispensable.
I would also like to acknowledge the individuals who aided with medical imaging; Joe Gati, Oksana
Opalevy and Joseph Umoh.
I would also like to thank the following individuals for their contributions and advice; Larry Chen for his training with the loading device and help troubleshooting, Carly Fennel for her advice and support, Felipe
Garcia and Adele Changoor for their help in the initial project planning and testing phase, Lucia Costanzo and Simone Holligan for their input into the statistical analysis completed.
I was very grateful to have the chance to be part of the CIHR Joint Motion Program (JuMP) from Western
University. The experience I have gained from this program has been invaluable.
Lastly, I would like to sincerely thank all those individuals who donate their body to further scientific research.
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Contents Acknowledgements ...... iii 1.0 Introduction and Background ...... 1 1.1 Research Problem Statement ...... 1 1.2 Osteoarthritis ...... 2 1.3 Anatomy of the knee joint ...... 2 1.4 Anatomy and Biomechanics of the Meniscus ...... 3 1.5 Meniscal Degeneration and Injury ...... 6 1.6 Meniscal Allograft Transplant (MAT) ...... 9 1.6.1 Extrusion ...... 10 1.6.2.1 Soft Tissue Fixation ...... 11 1.6.2.2 Bone Plug Fixation ...... 12 1.6.2.3 Bone Bridge Fixation ...... 12 1.7 Biomechanical Properties of the Meniscus ...... 12 1.8 Measuring Strain in the Meniscus ...... 13 1.9 Objectives ...... 20 1.10 References ...... 21 2.0 Chapter 2: Analysis of 3D Strain in the Human Medial Meniscus ...... 26 2.1 Abstract ...... 26 2.2 Introduction ...... 26 2.3 Methods ...... 28 2.3.1 Specimen Preparation ...... 28 2.3.2 Imaging ...... 28 2.3.3 Repeatability ...... 28 2.3.4 Analysis ...... 29 2.3.5 Statistical Analysis ...... 30 2.4 Results ...... 31 2.5 Discussion ...... 33 2.6 Conclusion ...... 35 2.7 Acknowledgements ...... 35 2.8 References ...... 36 3.0 Chapter 3: 3D Strain in Native Medial Meniscus Compared to Meniscus Allograft Transplant ...... 38 3.1 Abstract ...... 38 v
3.2 Introduction ...... 38 3.3 Methods ...... 41 3.3.1 Specimen Preparation ...... 41 3.3.2 MAT Procedure ...... 42 3.3.3 Imaging ...... 43 3.3.4 Analysis ...... 43 3.3.5 Statistical Analysis ...... 45 3.4 Results ...... 45 3.5 Discussion ...... 48 3.6 Conclusion ...... 51 3.7 Acknowledgements ...... 51 3.7 References ...... 52 4.0 Chapter 4: Conclusions and Recommendations ...... 54 4.1 References ...... 58 5.0 Appendix A ...... 59 5.1 Determining the Tibial Coordinate System and Calculating Strain ...... 59
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List of Figures
Chapter 1 Figure 1.1: Anatomy of the Knee Joint………………………………………………..……………..……..3 Figure 1.2: Anatomy of the Meniscus………………………………………………………..…………...... 4 Figure 1.3: Organization of collagen in the meniscus…………………………………………….……..…5 Figure 1.4: Types of Meniscus Tears…………………………………………………………………….....7 Figure 1.5: Meniscal Repair Techniques…………………………………………………………………...9 Figure 1.6: Meniscal Extrusion……………………………………………………………………………10 Figure 1.7: Main MAT fixation methods……………………………………………………………....….12 Chapter 2 Figure 2.1: Tibial coordinate system and middle and posterior marker tetrahedron placement…………..30 Figure 2.2: Average strain...…………………………………………………………………………...…..32 Figure 2.3: Visual representation of average strain………………………………………………...……..33 Chapter 3 Figure 3.1: This diagram depicts the three tunnel surgical fixation technique…………..…...... ……42 Figure 3.2: Average strain middle…………………………………………………………………....……46 Figure 3.3: Average strain posterior……………………………………………………………...……….46 Figure 3.4: Average percent extrusion…………………………………………………….…………...….47 Figure 3.5: Average linear extrusion…………………………………………………….…………...……47 Appendix A Figure A.1: Coronal view center...... …………………………………………………………………..….59 Figure A.2: Sagittal view tibial center……………………………………………………………….....…59 Figure A.3: Medial point - femoral contact center…………………………………………………...... ….60 Figure A.4: Lateral point - femoral contact center……………………………………………………...…60 Figure A.5: Distal center………………………………………………………………………………..…60
1
1.0 Introduction and Background
1.1 Research Problem Statement
Osteoarthritis is the most prevalent form of arthritis. 59 It is caused by the deterioration of cartilage within a joint; and can cause pain, swelling and stiffness. 59 It occurs commonly in weight bearing joints such as the knee. The meniscus is a soft tissue pad within the knee joint which reduces friction and helps distribute load. Injury or wear and tear of the meniscus of the knee is a risk factor for the progression of osteoarthritis in the knee joint. 37 It is also known that full or partial removal of the meniscus will lead to further progression of osteoarthritis, therefore, repair of the meniscus where possible is essential. 40, 51 If repair is not possible, a meniscal transplant is a viable treatment option. 46 Outlining mechanical properties, specifically strain, in the meniscus can help in diagnoses and assessment of injury or disease as well as help drive better rehabilitative and preventative measures. 33, 41 In addition, a strain measurement of the meniscus in its native environment, responding to physiological load, will enable tissue engineers to ensure that synthetic or engineered substitutes are functioning in an optimal manner. 11
Attempts to evaluate the strain in an intact meniscus under knee joint load have been developed using sensors embedded in the tissue, measuring deformation in MRI and using detailed tracking of voxel displacements in MRI.19, 55 This project evaluates a new method to measure meniscal strain in vitro by tracking implanted beads in the meniscus using medical image analysis of loaded and unloaded human cadaveric knee joints. This research will also investigate the application of this new method to evaluate the efficacy of meniscal allograft transplants compared to intact tissue, and simultaneously assess the effect of different surgical fixation techniques.
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1.2 Osteoarthritis
Osteoarthritis is a disease that affects all the tissues, including bone, cartilage, and soft tissues in an articulating synovial joint. It can cause pain, loss of mobility, swelling, stiffness and disability in affected individuals.59 It impacts more than 4.5 million people in Canada59 and more than 20 million in the United
States. 5 The financial impact for Canadians is $33 billion per year for arthritis conditions as a whole with osteoarthritis being the most prevalent type. 59 It is considered a leading cause of pain, functional limitation and disability. 59 Risk factors leading to the development and progression of osteoarthritis include age, genetics, joint injury, excess weight and complications from other diseases.59
1.3 Anatomy of the knee joint
The knee is a complex load bearing joint, (Figure 8), and is considered one of the largest and most complex joints in the body.69 It allows six degree of freedom rotation and translation while providing stability. It is held together by the bony architecture of the femur, tibia and patella as well as ligaments, capsule and musculature crossing the joint. 21 The hamstrings and quadriceps are the main muscle groups that control knee movement. The hamstrings on the posterior thigh contract to bend the knee while the quadriceps, located on the front of the thigh, contract to straighten the knee. 21 The main ligaments (soft tissue that connects bone to bone) of the knee are the medial and lateral collateral ligaments and the anterior and posterior cruciate ligaments. 21 The ends of the femur and tibia are also covered with cartilage which provides a smooth low friction surface and cushioning to help protect the knee. 21 The menisci of the knee sit on the tibial plateau and will be discussed further in the next section. 3
Figure 8.1: Anatomy of the Knee Joint 8
1.4 Anatomy and Biomechanics of the Meniscus
The menisci, (Figure 1.9), are two semi-lunar shaped fibrocartilaginous layers between the tibia and femur, one on the lateral side and one on the medial side of the knee joint. The meniscus acts to distribute
load, help stabilize the joint, reduce friction, increase lubrication, provide nutrients to the articular cartilage, and smooth movement between the incongruent surfaces of the tibia and femur. 40 4
Figure 1.9: Anatomy of the Meniscus 8
The meniscus considerably increases the contact area within the knee joint. In fact, a healthy meniscus takes up about 60% of the contact area which lowers the overall stress on the tibial and femoral cartilage. 23, 42 In vitro research has shown approximately 50% of the load placed on the knee is
transmitted through the meniscus depending on the flexion angle.55 The tibio-femoral contact area decreases by 4% for every 30° of flexion and the load on the meniscus changes as the knee flexes. At full flexion, the lateral meniscus is carrying 100% of the load on the lateral side and the medial meniscus is carrying 50% of the load on the medial side. 42
The composition of the meniscus is mainly collagen (type I) and water. Specifically, it comprises of
approximately 20% collagen fibres, 75% water and the final 5% is made up of multiple other substances
most notably proteoglycans. 60 The outer 10 – 25% of the meniscus is vascularized and therefore does have some healing capacity whereas the inner avascular tissue does not.42 There exist at least two
different cell populations within the meniscus. The fibrochondrocyte, which is surrounded by copious 5
extracellular matrix, is the main cell type found in the inner and middle of the tissue and the fibroblast-
like cells which form within a dense connective tissue and occupy the outer third of the meniscus. 24
The organization of collagen, see Figure 1.10, affects the transmission of forces through the tissue. The meniscal tissue is composed of circumferentially oriented collagen fibres in the bulk of the tissue, which mainly resist hoop stress, and radially oriented fibres at the surface which mainly resist shear stress. 4, 10
The surface layer of the tissue is varied with both radially and circumferentially oriented fibres. The deeper tissue consists of mainly circumferentially orientated collagen fibres with radial fibres holding them together. 45
The mechanical properties of the meniscal tissue are not consistent throughout the tissue due to the varying geometry, composition and attachments of the tissue. The posterior portion of the meniscus is both wider and thicker than the anterior portion, and has more attachments securing it to the tibial plateau. 55 There are also more radial fibres in the posterior section. The medial collateral ligament adds further stability to the middle section whereas the anterior is less restrained. 55
Figure 1.10: Organization of collagen in the meniscus 1) Superficial bundle network 2) lamellar layer 3) Circumferentially oriented fibre bundles 23 6
Favenesi et al. 17 and Spilker et al. 56 determined that the meniscus behaves like a biphasic material. This means that it can be analyzed and modeled as a solid matrix with an interstitial fluid phase. It is a viscoelastic material meaning it has a time-dependent response to load. 45 When a load is applied to the meniscus causing a displacement, the tissue will relax as fluid is pushed out and the load required to maintain that displacement will drop off over time. The rate of fluid movement out of the tissue depends on the viscosity of the interstitial fluid and the permeability of the meniscal tissue. 45 The fluid phase is able to carry a significant portion of the load due to the low permeability of the solid phase of the meniscus, which is comparably much lower than that of articular cartilage. 45
1.5 Meniscal Degeneration and Injury
Meniscal degeneration and injury is a common and debilitating issue. Research suggests that meniscal deficiency is one of the primary factors causing knee osteoarthritis, and meniscal preservation is a key factor for changing the trajectory of knee osteoarthritis.24 One of the main modes of meniscal injury is a tear, usually resulting from applied sudden force or trauma. 25 Meniscal tears can be classified as either traumatic or degenerative. Traumatic tears are tears occurring in a healthy meniscus due to a sudden force and degenerative tears are tears occurring as a result of deterioration over time. 66
Meniscal tears are also classified according to the geometry and orientation of the tear. The 3 main forms of meniscal tears are shown in Figure 1.11. Longitudinal tears follow the circumferential curve of the tissue, radial tears occur perpendicular to the curve and oblique tears occur at the edge of the tissue and are also known as “parrot beak” tears.
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Figure 1.11: Types of Meniscus Tears 69
The type, size, and location of the tear determine the effect on knee joint loading, risk of OA, healing capacity and repair options. 5, 21 Meniscus tears that cause extrusion of the meniscus beyond the edge of the tibial plateau and decrease contact area, and radial tears more than a third of the width are a greater risk factor towards the development of OA. 5, 21
Vascularity of the tissue is a main contraindication for repair of tears in the meniscus. 24 The red zone
(Figure 1.11) is the vascularized region of the meniscus which means it has blood flow and better healing
capacity and the white zone is the avascular region which means it lacks blood and has very limited
healing capacity. 69 Tears that extend into the white zone are more problematic due to the reduced healing
capacity.
It has been found that approximately 85% of osteoarthritis patients also exhibited severe meniscal degeneration.5 For meniscal tears specifically, Lohmander et al.39 estimated a frequency of occurrence of
70 per 100 000 people in Denmark. It was also noted in this study that meniscal injuries are more likely to be underdiagnosed compared to other knee injuries. As well, a study by Harper et al. 23 found that 8
radial tears in the meniscus were observed in 15% of patients experiencing knee discomfort. More recent studies have found increased incidence of meniscal injuries. De Coninck et al. reported that meniscal injuries are now one of the highest frequency injuries seen in orthopaedics. 15 Specifically in Sweden alone, 200 000 meniscal surgeries are completed each year. 39 In the USA, in 2013, it was estimated that there are 850 000 meniscus related surgeries performed per year. 66
When it comes to repairing meniscal tears, there are many different repair techniques but an inside-out or outside-in suturing technique has been the most often performed in recent time since open knee with sutures only was most common.70 The main types, (Figure 1.12), can be categorized into four sections including inside out, outside in, all inside and hybrid repairs. 29 The inside-out technique involves one suture passed through the superior and inferior surface of the meniscus and knotted on the outside of the capsule.29 The outside-in technique, which is recommended for mid or anterior third meniscal tears, involves two sutures passed through the superior and inferior surface of the meniscus and knotted on the outside of the capsule. 29 The all-inside technique is recommended for posterior horn tears to reduce the chances of neurovascular injury and improve healing and involves a type of suture hook that is passed through the posterior horn for all inside ligation.29 Hybrid repairs involve any new types of sutures or devices supplementing previous techniques in any of these categories. 29
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Figure 1.12: Meniscal Repair Techniques 50
Treatment options for severe meniscal injuries include meniscectomy; the full or partial removal of meniscal tissue. This is conducted when there is irreparable deterioration or injury. A study by Baker et al. 6 found that, in the general population, the incidence of meniscal injuries leading to meniscectomy was
61 in 100 000 in the US. This procedure can offer significant pain relief in the short term, 2 however; it
has been known since 1948 that meniscectomy causes negative changes in the joint mechanics leading to
osteoarthritis.16 It is now well known that full or partial meniscectomy will cause pain and degeneration
in the knee joint due to disruption of load distribution, increased contact stress and loss of stability. 15, 43
Therefore, there has been greater focus on studying the function of the meniscus and its repair in order to
avoid meniscectomy. 40
1.6 Meniscal Allograft Transplant (MAT)
Meniscal allograft transplantation is a replacement of the meniscal tissue with implanted cadaveric donor tissue. MAT can reduce pain and help restore function for patients who are symptomatic following a full or partial meniscectomy. 15, 43 Research suggests more data is needed regarding the long term
effectiveness of transplanted menisci. 15, 40
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1.6.1 Extrusion
A common complication related to MAT is extrusion of the allograft outside the boundaries of the tibial
plateau (Figure 1.13).40 This has been found to occur in anywhere from 26% to 75% of cases depending on how extrusion was measured in the study. 51 Meniscal extrusion will likely compromise the function of
the MAT and increases the risk of failure of the graft through degeneration or tears. 40 This is because extrusion reduces the contact area within the joint and causes an increase in stress due to the loss of load distribution and stability. 22 Meniscal extrusion occurs most frequently in the anterior horn or mid-
body 22 and is more frequent in lateral compared to medial MAT.51 A study by Abat et al. states that
3 mm past the edge of the tibial plateau is the usual threshold outside which meniscal extrusion is believed to be pathologic. 1 This measurement, however, can be subjective and observer-dependent. It also varies based on the size of the menisci. Rating the amount of meniscal extrusion as a percent of meniscal body width may further standardize results. 1
Figure 1.13: Meniscal Extrusion 15
Other studies have found this to be a trivial cut off point; extrusion greater than 3 mm has been noted 6 weeks post MAT with no further change in extrusion one year post MAT. 36 Furthermore, studies have found that the amount of meniscal extrusion did not increase over time post-surgery and may not lead to 11
further extrusion or degeneration. 36, 37 It has also not been proven to have any adverse effect on clinical or functional outcomes (Lysholm score). 22, 46, 51
Extrusion may be due to size mismatching or surgical error in positioning. 35, 36 A relationship has been found between sizing and extrusion. If the dimensions of the MAT are reduced by 5%, the rate of extrusion is also reduced significantly with no notable effects on clinical or radiographic outcomes. 27
Thus extrusion may be due to a variety of factors. Extrusion has not been found to be linked to the method of fixating the MAT yet it is still used as a comparative measure for chondroprotective effect.32
Since meniscal extrusion does not measure loss of load sharing directly, and due to the lack of consensus on the use of meniscal extrusion as on outcome measure, a more objective standardized method of evaluation is required.
1.6.2 Surgical Fixation of the Allograft
The ability of the allograft to produce beneficial results is highly dependent on proper size of the graft and fixation techniques. 2, 37, 40 Sizing is dependent on the tissue available but there has not been any consensus on which MAT fixation technique is the most effective. 1,40,43 The three main methods of fixating the transplant, described below, are using bone plugs, a bone bridge and simpler soft tissue fixation. Within each of these methods there exist several variations which are dependent on the surgeon performing the procedure.
1.6.2.1 Soft Tissue Fixation
In general, soft tissue fixation involves the use of sutures placed around the outside edge of the meniscus fixing it to the joint capsule as shown in Figure 1.14 - A. It often includes small tunnels drilled through the tibia through which the sutures on the ends of the meniscus can be passed through and tied off to reconstitute the meniscotibial ligaments.1 12
1.6.2.2 Bone Plug Fixation
This procedure involves harvesting the donor meniscus with plugs of bone at each end maintaining the enthesis. 1 As shown in Figure 1.14 - B, the meniscal tissue is implanted into the host knee by the use of
sutures and can also be completed arthroscopically or with open technique. The outside edge is generally
sutured similar to soft tissue fixation and the bone plugs are usually sutured at the bottom with small
tunnels going through the tibia. 1
1.6.2.3 Bone Bridge Fixation
The bone bridge technique can also be performed arthroscopically or with an open technique. 30 In general as shown in Figure 1.14 - C, the bone bridge technique is similar to the bone plug technique but instead of a small plug of bone taken with each end, a slot of bone with both ends of the meniscus attached is removed and implanted into the host knee. 40 This preserves proper spacing between the ends of the meniscus.
A B C
Figure 1.14: Main MAT fixation methods A) soft tissue B) bone plugs C) bone bridge 26
1.7 Biomechanical Properties of the Meniscus
Obtaining an accurate value of the biomechanical properties of the meniscus is important due to the need
for these properties in modeling tibiofemoral contact. 11 Determining the mechanical properties and 13
contact stresses in healthy tissue can also serve as a starting point for outlining the onset and progression of disease and lead to better recommendations for disease prevention.33, 41
Equally important is the need for quantitative data defining the biomechanical response of the meniscus to evaluate repair techniques and develop synthetic allografts that can properly mimic the function of the meniscus. 11 Donor meniscal allografts are currently the preferred treatment for meniscectomy patients, however, there are problems associated with their use including graft availability, cost, sizing, disease transmission, and lack of durability. 66 Extrusion of the meniscus over the edge of the tibial plateau is a common issue with allografts and there is currently no consensus with regards to methods of fixating the tissue. 66 At this time, only one synthetic full meniscal replacement, NUsurface (Active Implants,
Tennessee, USA), has been approved for clinical trials.66 Continued advancements in synthetic materials based on the properties of the native meniscus, however, could help to address problems related to donor tissue use. 66
Currently, no widely accepted guidelines exist for appropriate rehabilitation period or activity level recommendations post-surgery. 40 There is insufficient research to support decisions regarding activity levels post-surgery. 38 As a result, patients are given a wide variety of range of motion and weight bearing recommendations.38 Determining strain in the meniscus under various loads could help provide a quantitative measure to drive appropriate rehabilitation time and activity recommendations post-surgery. 38
Quantitative values for strain in the meniscal tissue could also lead to determining some quantitative measures for risk of meniscal tear when the joint biomechanics are perturbed.38
1.8 Measuring Strain in the Meniscus
Strain is a measure of deformation relative to a reference point excluding rigid body movement. This is a change in shape or change in the distance between particles in a body. 54 In its simplest form, it is a 14
change in length divided by the original length presented as a unitless ratio or percent. Strain can be analyzed as finite or infinitesimal. Finite strain analysis is used for the large deformations that occur in soft tissues. Infinitesimal strain is an approximation of finite strain that can be used for rigid materials such as metals or concrete. 54
Stress in its simplest form is a force divided by a unit area. It is a measure of the internal forces in a body. 54 Stress and strain values can be plotted to calculate the Young’s Modulus of Elasticity which gives measure of the stiffness of the material or can be modelled to determine other mechanical parameters such as permeability. 45
Previous attempts have been made to measure strain in the meniscus in-vitro using sensors. Spencer
Jones et al.55 and Seitz et al.52 measured linear hoop strain in an intact knee joint by inserting strain gauges into the tissue through windows made in a cadaveric knee joint. Spencer Jones et al. used uniform vertical loading with 3 times body weight at 0 and 30 degrees of flexion and strains between 1.54
– 2.65% were found. Higher strains were found in the anterior and middle sections as compared to the posterior which is likely due to the increased stiffness and decreased mobility from the anterior compared to posterior sections.55 As well, the posterior section is wider, contains more radial fibres to constrain it, and has more attachments to the tibia to hold it firmly in place. 55 Seitz et al. used vertical loading with approximately 1 times body weight at 0, 30 and 60 degrees flexion to measure strain at the anterior and posterior horns of the meniscus to compare strain pre and post partial meniscectomy. This study found strain in the intact joint to be between 1 and 1.9 % with no significant changes with partial meniscectomy.
These studies were limited in that they only capture strain in one direction. It would be beneficial with the complex anatomy and motions of the knee joint to be able to calculate strain in multiple directions.
As well, the joint was loaded in the axial direction in the research by Spencer Jones et al. which does not allow any degrees of freedom for rotation or translational movement, and the loading scenario in the research by Seitz et al. only allowed 3 degrees of freedom. Thus, neither joint loading scenario accurately 15
simulates physiological loading. There are also concerns with the instrumentation used to measure strain, in that the strain gauge pin insertion into the tissue could affect the normal behaviour of the tissue by restraining the tissue at the insertion points. 67 These restraints would not allow for strain variations at different depths in the tissue because the superficial tissue could restrict or cause extra movement of the movement of the pins.67
MRI evaluation of meniscal movement and deformation has been studied in vivo and in vitro within human and equine joints and can give a simplified two-dimensional measure of axial deformation in an intact meniscus. 18, 44, 9, 61 A range of axial deformations of 0.34 – 4 mm were found for human menisci at the anterior and posterior horns with approximately 1 body weight at varying flexion angles but did not report the initial height. A later study by De Coninck et al 14 performed similar in vivo MRI measurements to evaluate the movement and deformation of an artificial meniscus implant. This method was able to demonstrate differences in anterior-posterior movement between the native meniscus and the implant but showed no significant difference in the radial displacement or height. Both the native menisci and the implant have a range of axial deformations of 0.27 – 0.79 mm but did not report the initial height.
Advancements in MRI technology has allowed for new research using 3D MRI analysis to quantify in vivo deformation of human menisci under load. 41, 3 3D models were created from automatic or semi- automatic segmentation of images to calculate changes in dimensions. Preliminary results from MacLeod et al.41 suggest it is possible to use this method to evaluate differences between normal and osteoarthritic patients but more data is needed. Amano et al.3 even used this method to evaluate tears in menisci to help recommend appropriate treatment options. This method, however, does not allow for any examination of strain distribution within the meniscus.
16
These techniques have also been applied to measure cartilage strain. Sutter et al.58 used MRI to examine in vivo human cartilage strain from hopping activities. Manual segmentation was used to outline the boundaries of the condyles and cartilage thickness measurements were taken perpendicular to the surface to develop a map of the cartilage strain pattern. This technique could also be used to examine changes in cartilage due to meniscal injuries. 58
A more complete look at the 3D strain throughout the meniscus using MRI was done by Freutel et al.19 on porcine menisci. This study evaluated the 3D displacement field of the whole intact meniscus throughout the tissue and its attachments. FEA of the MRI data measured the specific strain field using a custom voxel-based mesh and volumes were registered of specific compartments of the meniscus to measure movements of the center of mass of each compartment. The highest strain was found to occur in the center of the meniscus. An average axial deformation of 11.6% was found at 2 times body weight.
Kessler et al. 28 assessed the non-linear strain patterns in human menisci using electronic speckle pattern interferometry on semi-confined meniscal cross sections under compression. As with Freutal et al., the highest strain was found to occur in the center of the meniscus with the lowest strain occurring at the femoral surface. As well, strain in older menisci was found to be higher than strain calculated in younger menisci. Only cross sections taken from the posterior third of the meniscus were evaluated so no comparisons between anterior to posterior strain distributions were drawn as in Spencer Jones et al.55
Peak compressive strain in response to a 10 µm increments in older menisci was 0.33% and 0.25% in younger menisci. It is interesting to note that non-uniform strain distributions were found. The fact that the meniscus was cut into cross sections disrupting the circumferential fibres and the fact that the cross section remained unconstrained would affect the results obtained. As well, the normal tibial and femoral surfaces and lateral boundary were replicated with rigid holders that may not adequately simulate 17
physiological conditions. As noted in the paper, these results may not be representative of physiological values but give a comparison of strain distribution across cross-sections.
Tissakht et al.60 performed uniaxial elongation tests on various regions and layers within the meniscus both circumferentially and radially to determine the elastic modulus, the maximum strain and the strain intersect. The strain intersect on the stress strain curve is the assumed point at which the first fibre becomes taught during tensile loading. This study analyzed the meniscus as a composite, an incompressible hydrophilic matrix with embedded collagen fibres. They found that for radially oriented samples, the elastic modulus was in the range of 2.03 – 22.62 MPa. For the circumferential specimens, the maximum strain before failure was in the range of 17.15 – 34.10%. There were no significant changes between different regions of the meniscus (ie., anterior vs. posterior) but the inner layer of the tissue had a lower elastic modulus then the outer proximal and distal surfaces. The maximum strain, before failure, was determined to be within the range of 20.82% - 60.62% with higher strains found in the anterior and middle regions as opposed to posterior. As well, the inner layer of the tissue also exhibited higher strain following the trend of the elastic modulus.
Chia and Hull,11 measured axial and radial compressive moduli under unconfined compression in in-vitro human menisci in the anterior, middle and posterior sections at equilibrium and a physiological strain rate approximated for walking. This study found that the ratio between the axial and radial compressive moduli are the same at equilibrium (83.4kPa and 76.1kPa respectively) and at a rate of strain equivalent to walking (718 kPa and 605 kPa). It was also found that calculations of tension versus compression result in large variances in the modulus. This study also noted increased stiffness in the anterior of the meniscus similar to Danso et al. 13 The results of this study reinforce the idea that a transverse plane of isotropy exists for the mechanical properties of the meniscus. This study did find changes in modulus at different strain levels.
18
Meniscal indentation can also be used to obtain mechanical properties of the surface of the tissue. Danso et al. 13 conducted indentation testing on full intact human menisci. Many studies have used resected cylinders or cubes of tissue to compare mechanical properties from different areas of the meniscus, however, cutting through the meniscus may loosen the collagen fibril tension affecting its response to load.13 This study found no significant differences in properties in different sites on the lateral meniscus but did find significantly increased stiffness in the anterior of the medial meniscus and more variation of mechanical properties such as permeability. The anterior horn of the medial meniscus has a decreased width compared to the rest of the tissue but likely contains the same number of collagen fibres which would account for the changes in properties. 34 Indentation was performed at 20% of the thickness of the meniscus at the respective site and therefore mainly captures superficial tissue properties but also captures some of the lamellar region and central main layer.
A study by Wang et al.68 attempted to elucidate the dynamic contact mechanics in vitro on the meniscus during gait in an intact knee and after two different methods of surgical fixation for meniscal allograft transplants. This study found that in the intact knee the peak contact stress was 4.2 ± 1.2 MPa with a corresponding contact area of 546 ± 132 mm 2. The knees were loaded axially and therefore the knee was restricted from rotating and translating as it normally would during flexion. A pressure sensor on the medial tibial plateau measured the contact mechanics. This type of measurement does not closely resemble physiologic loading. It is invasive as it requires removal of the patella and extensor mechanisms and it as it is unknown to what degree the addition of the sensor disrupts normal contact mechanics.
Bedi et al.7 notes that contact mechanics of the knee joint are dependent on direction and magnitude and dynamic testing representative of physiologic loads are needed to accurately measure joint contact pressure relating to meniscal treatment. This study used a dynamic gait simulator with cadaveric knees to compare the contact pressure. However, the pressure was measured with sensors inserted into the joint.
The insertion of sensors is invasive and may inadvertently alter the normal soft tissue mechanics. Pozzi et 19
al.48 noted as a limitation in their study of knee contact mechanics that insertion of sensors into the joint was only achieved with incision of other attachments to the menisci which may be important to load transmission. Pozzi et al. 48 measured the strain in the intact and partially resected meniscus statically with the use of transducers similar to Spencer Jones et al.55 Similar studies where the joint is preserved by evaluation using medical imaging are needed to validate these findings due to the loss of these attachments and the potential changes in joint mechanics.
New methods of measurement of mechanical properties are being developed. Implanted small diameter
(<1 mm) metal beads have been used as markers to calculate strain in soft tissue. A study by Lin et al.38 demonstrated the use of tracking bead movement in meniscal tissue using biplanar radiography as a viable method for calculating linear strain across meniscal tears. This study found that at high degrees of flexion a circumferential tear will compress inwards rather than gap. However, this study was limited as it only calculated one dimensional strain. A technical note by Innes et al.25 also proposed the use of beads to calculate strain but used strain tensors to calculated three dimensional strain in the tissue. This preliminary study found larger average principal strains in the anterior of the meniscus of 21%. Average principal strains in the posterior region were approximately 28% lower. Results suggested that this would be a feasible method for a more detailed analysis.
Waldman et al.67 conducted a study measuring the finite normal and shear strains in the ventricular wall of a canine heart. Lead beads of 1 mm diameter were implanted in a tetrahedral formation with fixed reference points. High speed biplane cineradiography was used to obtain the three dimensional coordinates of each bead. Using this method, the study was able to measure changes in strain at varying depths in the tissue.
20
There is a gap in knowledge with respect to the biomechanical response and function of the meniscus.
Currently, no study has calculated three dimensional strain in a minimally invasive way in an intact human meniscus with an intact joint capsule and physiologically relevant loading and flexion.
With the subjectivity of measurements of meniscal extrusion and the lack of consensus in the importance of extrusion in evaluating different fixations of MAT, there is a need for an objective and standardized method of comparing different surgical techniques for improved long term results of MAT.
1.9 Objectives
The objectives of this research are:
• To evaluate the use of implanted beads in an intact cadaveric knee meniscus under
physiologically relevant loading to calculate meniscal strain
• To use this method to determine if there are any measurable changes in the strain of the intact
meniscus compared to implanted meniscal allografts using different surgical fixation techniques.
• To compare the degree of meniscal extrusion in the MAT between the two surgical fixation
techniques.
21
1.10 References
1. Abat, F., Gelber, P.E., Erquicia, J.I., Pelfort, X., Gonzalez-Lucena, G., Monllau, J.C., 2012. Suture-Only Fixation Technique Leads to a Higher Degree of Extrusion Than Bony Fixation in Meniscal Allograft Transplantation. Am. J. Sports. Med. 40, 1591-1596. 2. Alentorn-Geli, E., Vazquez, R.S., Balletbo, M.G., Diaz, P.A., Steinbacher, G., Segarra, X.C., Vilarrubia, M.R., Bertameu, R.C., 2011. Arthroscopic meniscal allograft transplantation without bone plugs. Knee. Surg. Sports. Traumatol. Arthrosc. 19, 174-182. 3. Amano, H., Iwahashi, T., Suzuki, T., Mae, T., Nakamura, N., Sugamoto, K., Shino, K., Yoshikawa, H., Nakata, K., 2015. Analysis of displacement and deformation of the medical meniscus with a horizontal tear using a three dimensional computer model. Knee. Surg. Sports. Traumatol. Arthrosc. 23(4), 1153-1160. 4. Aspden, R.M., Yarker, Y.E., Hukins, D.W.L., 1985. Collagen orientations in the meniscus of the knee joint. J. Anat. 140(3), 371-380. 5. Badlani, J.T., Borrero, C., Golla, S., Harner, C.D., Irrgang, J.J., 2013. The Effects of Meniscus Injury on the Development of Knee Osteoarthritis. Am. J. Sports. Med. 41(6), 1238-1244. 6. Baker, B.E., Peckham, A.C., Pupparo, F., Sanborn, J.C., 1985. Review of Meniscal Injury and Associated Sports. Am. J. Sports. Med. 13(1), 1-4. 7. Bedi, A., Kelly, N., Baad, M., Fox, A.J.S., Ma, Y., Warren, R.F., Maher, S.A., 2012. Dynamic Contact Mechanics of Radial Tears of the Lateral Meniscus: Implications for Treatment. Arthroscopy. 28(30), 372-381. 8. Cartilage Restoration Center of Indiana. Knee Joint Anatomy. N.p.: The Cartilage Center. 2015. Web. March 30 2015. 9. Chen, H., Yang, K., Dong, Q., Wang, Y., 2014. Assessment of tibial rotation and meniscal movement using kinematic magnetic resonance imaging. J. Orthop. Surg. Res. 9, 65-68. 10. Chen, L., Gordon, K.D., Hurtig, M., 2014. Design and validation of a cadaveric knee joint loading device compatible with magnetic resonance imaging and computed tomography. Med. Eng. Phys. 36(10), 1346-51. 11. Chia, H.N., Hull, M.L., 2007. Compressive Moduli of the Human Medial Meniscus in the Axial and Radial Directions at Equilibrium and at a Physiological Strain Rate. J. Orthop. Res. 26(7) Online. 12. Cole, B.J., Fox, J.A., Lee, S.J., Farr, J., 2003. Bone Bridge in Slot Technique for Meniscal Transplantation. Op. Tech. Sports. Med. 11(2), 144-155. 13. Danso, E.K., Makela, J.T.A., Tanska, P., Mononen, M.E., Honkanen, J.T.J., Jurvelin, J.S., Toyras, J., Julkunen, P., Korhonen, R.K., 2015. Characterization of site-specific biomechanical properties of human meniscus – Importance of collagen and fluid on mechanical nonlinearities. J. Biomechanics. In Press. 14. De Coninck, T., Elsner, J.J., Linder-Ganz, E., Cromheecke, M.S., Huysse, W., Verdonk, R., Verstraete, K., Verdonk, P., 2014. In-vivo evaluation of the kinematic behaviour of an artificial medial meniscus implant: A pilot study using open MRI. Clin. Biomech. 29(8), 898-905. 15. De Coninck, T., Huysse, W., Verdonk, R., Verstraete, K., Verdonk, P., 2013. Open Versus Arthroscopic Meniscus Allograft Transplantation: Magnetic Resonance Imaging Study of Meniscal Radial Displacement. Arthroscopy. 29(3), 514-521. 22
16. Fairbank, T.J., 1948. Knee Joint Changes After Meniscectomy. J. Bone. Joint. Surg. 30b(4), 664- 670. 17. Favenesi, J.A., Schaffer, J.C., Mow, V.C., 1983. Biphasic mechanical properties of the knee meniscus. Orthop. trans. 8, 264. 18. Fowlie, J.G., Arnoczky, S.P., Stick, J.A., Pease, A.P., 2011. Meniscal Translocation and deformation throughout the range of motion of the equine stifle joint: an in vitro cadaveric study. Equine. Vet. J. 43(3), 259-64. 19. Freutel, M., Seitz, A.M., Galbusera, F., Bornstedt, A., Rasche, V., Knothe, Tate. M.L., Ignatius, A., Durselen, L., 2015. Analysis of displacement and deformation of the medial meniscus with a horizontal tear using a three-dimensional computer model. Knee. Surg. Sports. Traumatol. Arthrosc. 23, 1153-1160. 20. Gale, D.R., Chaisson, C.E., Totterman, S.M.S., Schwartz, R.K., Gale, M.E., Felson, D., 1999. Meniscal Subluxation: Association with Osteoarthritis and Joint Space Narrowing. Osteoarthr. Cartilage. 7, 526-532. 21. Goldblatt, J.P., Richmond, J.C., 2003. Anatomy and Biomechanics of the Knee. Oper. Techn. Sport. Med. 11(3), 172-186. 22. Ha, J.K., Shim, J.C., Kim, D.W., Lee, S.K., Ra, H.J., Kim, J.G., 2010. Relationship Between Meniscal Extrusion and Various Clinical Findings After Meniscus Allograft Transplantation. Am. J. Sports. Med. 38, 2448. 23. Harper, K.W., Helms, C.A., Lambert, H.S., Higgins, L.D., 2005. Radial Meniscal Tears: Significance, Incidence, and MR Appearance. A.J.R. 185, 1429-1434. 24. Hutchinson, I.D., Moran, C.J., Potter, H.G., Warren, R.F., Rodeo, S.A., 2013. Restoration of the Meniscus Form and Function. Am. J. Sports. Med. 42-4. 25. Innes, M., Tschirhart, C.E., McErlain, D.D., Holdsworth, D.W., Gordon, K.D., Hurtig, M., 2011. A novel technique for quatifying three-dimensional meniscal strain. J. Bone. Joint. Surg. Br. 93-B no. SUPP III 248. 26. Jackson, D.W. (interviewer), Goble, M. (interviewee), 2003. Meniscal allograft transplantation: When and how to proceed. Healio Orthopedicstoday. Retrieved from http://www.healio.com/orthopedics/knee/news/print/orthopedics-today/%7Bc4c01fbe-ab5f-46d0- 8f6b-d66c76092ceb%7D/meniscal-allograft-transplantation-when-and-how-to-proceed. 27. Jang SH, Kim JG, Ha JG, Shim JC. Reducing the size of the meniscal allograft decreases the percentage of extrusion after meniscal allograft transplantation. Arthroscopy 2011;27:914–922. 28. Kessler, O., Sommers, M., Augustin, T., Haybaeck, J., D’Lima, D.D., Madey, S,M., Bottlang, M., 2015. Higher strains in the inner region of the meniscus indicate a potential source for degeneration. J. Biomech. ahead of print. 29. Keyhani, S., Abbasian, M.R., Siatiri, N., Sarvi, A., Kivi, M.M., Esmailiejah, A.A., 2015. Arthroscopic Meniscal Repair: “Modified Outisde-In Techniques.” Arch. Bone. Jt. Surg. 3(2), 104-108. 30. Kim, J.M., Lee, B., Kim, K.H., Kim, K.A., Bin, S.I., 2012. Results of meniscus allograft transplantation using bone fixation: 110 cases with objective evaluation. Am. J. Sports. Med. 40(5), 1027-34. 31. Kim, J.M., Shim, J.C., Kim, D.W., Lee, Y.S., Ra, H.J., Kim, J.G., 2010. Relationship between meniscal extrusion and various clinical findings after meniscus allograft transplantation. Am. J. Sports. Med. 38(12), 2448-2455. 23
32. Koh YG, Moon HK, Kim YC, Park YS, Jo SB, Kwon SK. Comparison of medical and lateral meniscal transplantation with regard to extrusion of the allograft, and its correlation with clinical outcome. J Bone Joint Surg Br 2012;94-B:190-3. 33. Lai, J.H., Levenston, M.E., 2010. Meniscus and Cartilage Exhibit Distinct Intra-Tissue Strain Distributions Under Unconfined Compression. Osteoarthr. Cartilage. 18(10), 1291-1299. 34. Lechner, K., Hull, M.L., Howell, S.M., 2000. Is the circumferential tensile modulus within a human medial meniscus affected by the test sample location and cross-sectional area? J. Orthop. Res. 18(6), 945-51. 35. Lee DH, Kim JM, Lee BS, Kim KA, Bin S. Greater axial trough obliquity increases the risk of graft extrusion in lateral meniscus allograft transplantation. Am J Sports Med 2012;40:1597–1605
36. Lee DH, Kim TH, Lee SH, Kim CW, Kim JM, Bin S. Evaluation of meniscus allograft transplantation with serial magnetic resonance imaging during the first postoperative year: focus on graft extrusion. Arthroscopy 2008;24:1115–1121 37. Lee, J.J., Choi, C.J., Choi, Y.J., Choi, C.H., 2010. Magnetic Resonance Imaging Evidence of Meniscal Extrusion in Medial Meniscus Posterior Root Tear. Arthroscopy. 26(12), 1602-1606. 38. Lin, D.L., Ruh, S.S., Jones, H.L., Karim, A., Noble, P.C., McCulloch, P.C., 2013. Does High Knee Flexion Cause Separation of Meniscal Repairs? Am. J. Sports. Med. 41(9), 2143-2150. 39. Lohmander, L.S., Englund, P.M., Dahl, L.L., Roos, E.M., 2007. The Long-term Consequence of Anterior Cruciate Ligament and Meniscus Injuries. Am. J. Sports. Med. 35(10), 1756-1769. 40. Lubowitz, J.H., Verdonk, P.C.M., Reid, J.B., Verdonk, R., 2007. Meniscus allograft transplantation: a current concepts review. Knee. Surg. Sports. Traumatol. Arthrosc. 15, 476-492. 41. MacLeod, T.D., Subburaj, K., Wu, S., Kumar, D., Wyatt, C., Souza, R.B., 2015. Magnetic resonance analysis of loaded meniscus deformation: a novel technique comparing participants with and without radiographic knee osteoarthritis. Skeletal. Radiol. 44(1), 125-35. 42. Makris, E.A., Hadidi, P., Athanasiou, K.A., 2011. The knee meniscus: Structure-function, pathophysiology, Current repair techniques and prospects for regeneration. Biomaterials. 32, 7411-7431. 43. Marcacci, M., Zaffagnini, S., Muccioli, G.M.M., Grassi, A., Bonanzinga, T., Nitri, M., Bondi, A., Molinari, M., Rimondi, E., 2012. Meniscal Allograft Transplantation Without Bone Plugs : A 3- Year Minimum Follow-up Study. Am. J. Sports. Med. 40, 395. 44. Mastrokalos, D.S., Panayiotis, J., Papagelopoulos, J., Mavrogenis, A.F., Hantes, M.E., Paessler, H.H., 2008. Changes of the posterior meniscal horn height during loading: An in vivo magnetic resonance imaging study. Orthpedics. 31, 1. 45. McDermott, I.D., Masouros, S.D., Amis, A.A., 2008. Biomechanics of the menisci of the knee. Current Orthopaedics. 22, 193-201. 46. Myers P, Tudor F. Meniscal Allograft Transplantation: How Should We Be Doing It? A Systematic Review. Arthroscopy. 2015;31(5)911-925. 47. Petersen, W., Tillmann, B., 1998. Collagenous fibril texture of the human knee joint menisci. Anat Embryol (Berl). 197, 317-324. 48. Pozzi, A., Tonks, C.A., Ling, H.Y., 2010. Femorotibial Contact Mechanics and Meniscal Strain after Serial Meniscectomy. Veterinary. Surg. 39(4), 482-488. 24
49. Richards, D.P., Barber, F.A., Herbert, M.A., 2005. Compressive Loads in Longitudinal Lateral Meniscus Tears: A Biomechanical Study in Porcine Knees. Arthroscopy. 21(12), 1452-1456. 50. Sabat, D., (May 11, 2014). Arthroscopic Meniscus Surgery: Resect or Repair 2014 . Retrieved from http://www.slideshare.net/drdsabat/meniscus-tear-resect-or-repair-2014 51. Samitier, G., Alentorn-Geli, E., Taylor, D.C., Rill, B., Lock, T., Moutzouros, V., Kolowich, P., 2015. Meniscal allograft transplantation. Part 1: systematic review of graft biology, graft shrinkage, graft extrusion, graft sizing, and graft fixation. Knee. Surg. Sports. Traumatol. Arthrosc. 23, 310-322. 52. Seitz, A.M., Lubomierski, A., Friemert, B., Ignatius, A., Durselen, L., 2011. Effect of Partial Meniscectomy at the medial posterior horn on tibiofemoral contact mechanics and meniscal hoop strains in human knees. J. Orthop. Res. 30(6), 934-42. 53. Sekiya, J.K., West, R.V., Groff, Y.J., Irrgang, J.J., Fu, F., Harner, C.D., 2006. Clinical Outcomes Following Isolated Lateral Meniscal Allograft Transplantation. Arthroscopy. 22(7), 771-780. 54. Spencer, A. J. M., 2004. Continuum Mechanics. Dover Publications, Inc. Mineola, New York, pp. 70-74. 55. Spencer Jones, R., Keene, G.C.R., Learmonth, D.J.A., Bickerstaff, D., Nawana, N.S., Costi, J.J., Pearcy, M.J., 1996. Direct Measurement of Hoop Strains in the Intact and Torn Human Medial Meniscus. Clin. Biomech . 11(5), 295-300. 56. Spilker, R.L., Donzelli, P.S., Mow, V.C., 1992. A Transversely isotropic biphasic finite element model of the meniscus. J. Biomech. 25, 1027-45. 57. Sun, Y., Mauerhan, D.R., Honeycutt, P.R., Kneisl, J.S., Norton, J.H., Hanley, E.N., Gruber, H.E., 2010. Analysis of meniscal degeneration and meniscal gene expression. B.M.C. Musculoskel. Dis. 11(19), 1471-1474. 58. Sutter, E.G., Widmyer, M.R., Utturkar, G.M., Spritzer, C.E., Garrett, W.E., DeFrate, L.E., 2015. In vivo measurement of localized tibiofemoral cartilage strains in response to dynamic activity. Am. J. Sports. Med. 43, 370. 59. The Arthritis Society. Osteoarthritis . N.p.: Arthritis Society. 2011. Web. 03 July 2013. 60. Tissakht, M., Ahmed, A.M., 1995. Tensile Stress-Strain Characterics of the Human Meniscal Material. J. Biomechanics. 28(4), 411-422. 61. Vedi, V., Williams, A., Tennant, S.J., Spouse, E., Hunt, D.M., Gedroyc, W.M.W., 1999. Meniscal movement an in-vivo study using dynamic MRI. J. Bone. Joint. Surg. [Br] 81-B, 37-41. 62. Verdonk, P.C.M., Forsyth, R.G., Wang, J., Almqvist, K.F., Verdonk, R., Veys, E.M., Verbruggen, G., 2005. Characterisation of human knee meniscus cell phenotype. Osteoarthr. Cartilage. 13(7), 548-560. 63. Verdonk, P.C.M., Verstraete, K.L., Almqvist, K.F., Cuyper, K.D., Veys, E.M., Verbruggen, G., Verdonk, R., 2006. Meniscal Allograft Transplantation: Long-term Clinical Results with Radiological and Magnetic Resonance Imaging Correlations. Knee. Surg. Sports. Traumatol. Arthrosc. 14, 694-706. 64. Verma, N.N., Kolb, E., Cole, B.J., Berkson, E., Garretson, R., Farr, J., Fregly, B., 2013. The Effects of Medial Meniscal Transplantation Techniques on Intra-Articular Contact Pressures. J. Knee. Surg. 21, 20-26. 65. Wajsfisz, A., Meyer, A., Makridis, K.G., Hardy, P., 2013. A new arthroscopic technique for lateral meniscal allograft transplantation: Cadaver feasibility study. Ortho. Trauma. 99, 299-304. 25
66. Vrancken, A.C.T., Buma, P., van Tienen, T.G., 2013. Synthetic meniscus replacement: a review. International Orthopaedics. 37, 291-299. 67. Waldman, L.K., Fung, Y.C., Covell, J.W., 1985. Transmural Myocardial Deformation in the Canine Left Ventricle Normal in Vivo Three-Dimensional Finite Strains. Circ. Res. 57, 152-163. 68. Wang, H., Gee, A.O., Hutchinson, I.D., Stoner, K., Warren, R.F., Chen, T.O., Maher, S.A., 2014. Bone Plug Versus Suture-Only Fixation of Meniscal Grafts. A.J.S.M. 42(7), 1682-1689. 69. WebMD. Knee Pain Health Center . N.p.: WebMD. 2015. Web. April 2015. 70. Xu, C., Zhao, J., 2012. A meta-analysis comparing meniscal repair with meniscectomy in the treatment of meniscal tears: the more meniscus, the better outcome? Knee. Surg. Sports. Traumatol. Arthrosc. 23, 164-170.
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Note: Chapter 2 has been submitted for publication in the Journal of Biomechanics
2.0 Chapter 2: Analysis of 3D Strain in the Human Medial Meniscus
2.1 Abstract
This study presents a method to evaluate three-dimensional strain in meniscal tissue using medical imaging. Strain is calculated by tracking small teflon markers implanted within the meniscal tissue using computed tomography imaging. The results are presented for strains in the middle and posterior third of the medial menisci of 10 human cadaveric knees, under simulated physiologically relevant loading. No statistically significant difference between strain in the middle or posterior of the meniscus or between the principal directions of strain is uncovered.
Keywords: Meniscus, strain, soft tissue biomechanics
2.2 Introduction
The meniscus is an integral component of the knee joint. It acts to distribute load, stabilize the joint, reduce friction, increase lubrication, and increase conformity between the surfaces of the tibia and femur. 11 Injury or wear and tear of the meniscus is a risk factor for the progression of osteoarthritis in the knee joint. Total meniscectomy (removal of the meniscus) can produce a 14-fold increase in the risk of developing osteoarthritis at 21 years following the procedure, therefore, repair or replacement of the meniscus where possible is essential. 20, 6 Outlining the structure-function relationship in the meniscus will aid in determining the onset and progression of disease. 8 In addition, an accurate, quantitative measure of the mechanical response of the meniscus to load is essential in the development of synthetic tissue replacements or repair techniques. 4
27
The strain response in an intact meniscus in vitro has been previously reported using sensors embedded in the tissue. 14, 15 These studies utilized uniaxial compression of the knee joint, which is a simplified model of physiological loading. The results are limited because the strain sensors are only capable of capturing uniaxial strain at one location. As well, the strain gauge pin insertion into the tissue could affect the normal behaviour of the tissue by restraining the tissue at the insertion points. 19 The complex anatomy and kinematics of the knee joint justifies a 3D strain measurement of the meniscus.
Magnetic resonance (MR) evaluation of meniscal movement and deformation has been studied both in- vivo and in-vitro. These methods can provide a simplified two- or three-dimensional measure of axial deformation measured directly from the image, but does not elucidate the distribution of strain within the tissue. 1, 2, 12, 17 A more complete look at the 3D strain throughout the meniscus using MRI was done by
Freutel et al. 5 on porcine menisci. The 3D displacement field of the whole intact meniscus was evaluated throughout the tissue and its attachments. The specific strain field was measured using a custom voxel- based mesh where specific compartments of the meniscus were given registered volumes to measure movements of the center of mass of each compartment. This method has not been studied in human menisci.
Lin et al. 9 studied linear strain in-vitro using implanted bead markers in human menisci. This was used to evaluate circumferential tears in the meniscus. To the author’s knowledge, no study has calculated 3D strain in an intact human meniscus with an intact joint capsule and physiologically relevant loading scenario.
This study evaluates a new method to measure meniscal strain in-vitro by tracking implanted markers in the meniscus using medical image analysis of loaded and unloaded human cadaveric knee joints. The intact strain distribution from 10 human cadaveric knee joints is summarized. 28
2.3 Methods
Ten fresh-frozen human cadaveric knees (average age 67, 5 male,) were evaluated using a novel loading device which is capable of applying repeatable positioning and loading of a human cadaveric knee joint using simulated muscle forces of the quadriceps and hamstrings. 3 Specimens were prepared for imaging as outlined below, positioned in pre-determined loading angles, followed by microcomputed tomography
(CT) imaging scans with and without a simulated muscle load applied.
2.3.1 Specimen Preparation
The knee joints were prepared as outlined in a previous publication. 3 Eight markers (Teflon beads, 0.8 mm, Salem Specialty Ball Co., CT, USA) were visually inserted in two approximate tetrahedral formations in the middle 1/3 and posterior 1/3 of the medial meniscus, Figure 1. This was completed under arthroscopic guidance performed by an experienced orthopaedic surgeon. The knee was manually manipulated through ten cycles of flexion and extension prior to testing. The joint was mounted into the loading device and set to 5° of flexion using a hand-held goniometer .
2.3.2 Imaging
Two images were acquired for each specimen using a 154 µm resolution volumetric cone-beam micro-CT scanner (GE Locus Ultra), one in an unloaded state and the other in a loaded state. Image acquisition time was approximately 16 seconds. Following the unloaded state, load was then applied to the knee joint via the muscle cables until a joint load of approximately body weight (650 ±160 N) was reached.
2.3.3 Repeatability
A separate knee joint (70 years, male) was used to evaluate the repeatability of this method. Five repeated loading trials and image acquisition sequences were conducted on this knee.
29
2.3.4 Analysis
To quantify the strain in the tissue, the centroid 3D coordinates of each marker were recorded using
MicroView 3D Image Viewer 2.5.0 (Parallax Innovations, open source software). To create a tibial coordinate system, anatomical landmarks were chosen from each image (Figure 1) (Appendix A). These landmarks were the center of the medial and lateral femoral contact areas on the tibial plateau, and the center most distal point on the tibia. The line from the lateral to medial landmark is the medial-lateral axis (positive medial) and the mid-point between those two points to the distal landmark is the superior- inferior axis (positive superior). A cross product of those two axes determines the anterior-posterior axis. Then another cross product of the superior-inferior and anterior-posterior axes is taken to form a new medial lateral axis to ensure all three axes are orthonormal. Marker coordinates were then transformed into this tibial coordinate system to establish anatomical directions for calculations of strain.
The 3D strain in the tissue was calculated from the unloaded and loaded marker positions as described in
Waldman et al. 19 The markers that formed the vertices of the tetrahedron were non-coplanar and defined a volume no greater than 9 mm 3. Preliminary results showed this to be a reasonable volume above which the results became erratic. The tetrahedron must be small enough that the tissue properties can be assumed to be homogeneous throughout. 19
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Figure 2.15: Tibial coordinate system and middle and posterior marker tetrahedron placement (M is the medial point chosen to develop the coordinate system, L is the lateral point and D is the distal tibial point described).
Six independent strains were obtained, three principal strains and three shearing strains, according to
Equation 1.
∆ ∆ 2 ∆ ∆ 1
Where ∆so is the original distance between the markers prior to loading and ∆s is the distance between the markers after loading, E is the strain, ∆ai is the distance from the first marker to the tibial coordinate
19 system and ∆aj is the distance from the second marker to the tibial coordinate system. This equation yields six algebraic equations which can be solved to obtain the six strain components of the symmetric strain tensor.
2.3.5 Statistical Analysis
Statistical analysis using a two-way ANOVA (IBM SPSS Statistics 22) was conducted with independent factors of tetrahedron position (middle, posterior) and principle strain direction (ML, AP, SI). This was 31
used to determine differences in strains between measurements in the middle versus the posterior of the meniscus and between the anatomical directions of the three principal strains.
2.4 Results
For the five repeatability trials, a maximum standard deviation of 2.51% was found for all six directions of strain.
Figure 2 shows the average 3D strain found in nine knees for the middle 1/3 and eight knees for the posterior 1/3 of the meniscus.
No statistically significant difference was found between the middle and posterior strains with an observed power of 8.2%. There were also no differences in principle strain magnitudes in each anatomical direction with an observed power of 50.0%.
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Figure 2.2: Average Strain profile from intact menisci (N=9 middle tetrahedron, N=8 posterior tetrahedron). Medial-
Lateral (ML), Anterior-Posterior (AP) and Superior-Inferior (SI) principal strains are shown, and directions ML/AP,
ML/SI and AP/SI indicate shearing strains. Error bars represent standard deviations.
Figure 3 provides a visual representation of the strains found in both the middle and posterior region to better indicate the direction and magnitude of strain found.
33
Figure 2.3: Visual representation of average strain magnitude and directions found plus/minus standard deviation (N=9 middle tetrahedron, N=8 posterior tetrahedron).
2.5 Discussion
This is the first study to quantitatively study regional 3D meniscal strain in a large number of human knees under simulated physiological loading. Knowledge of the 3D meniscal strain could lead to a quantitative measure for comparing surgical techniques, help replicate properties for synthetic allografts, provide a quantitative measure to outline the onset of disease and evaluate rehabilitation recommendations to improve and standardize procedures.
The results found for the 10 knees are expected as tibiofemoral loading of the meniscus results in hoop stresses, 11 which may result in fibres in the ML direction to be compressed and fibres in the AP direction to be pulled as the meniscus is mainly anchored at the anterior and posterior horn attachments. The tensile strain in the middle region of the meniscus in the SI direction is accompanied by the compressive strain in the ML direction. In the posterior region of the meniscus, the SI compression is accompanied with tensile strains in the AP direction. These results describe how the meniscus is responding and deforming to load. Although no significant difference in strain between the middle and posterior regions 34
were found, this may be uncovered under differing knee flexion angles due to increased strain on the posterior of the meniscus with increasing flexion angle. 15
There is a large degree of variability in meniscal strain measurements found in previous studies due to the broad range of methods used. Kessler et al. 7 used electron speckle patter interferometry on meniscal cross sections and found highly non-uniform strain distributions similar to this study, however, the values were much lower, potentially because of the additional restraints on the tissue. An aggregate strain of 0.14% strain was found and local compressive strains ranged from 0.03–0.7% for 10 µm compression. A study by Freutel et al. 5 found 3D strain distribution in porcine menisci using a new method tracking MRI voxel displacements and found an average radial stretch of 0.6%, an average circumferential stretch of 0.9% and an average compression of 11.6% with a load of 2 times body weight applied. Spencer Jones et al. 15 performed uniaxial loading and with strain gauges placed on the peripheral rim of the meniscus and measured circumferential strain with results of 1.54% in the posterior, 2.65% in the middle and 2.86% in the anterior for 3 times body weight.
The results of this study showed higher strains than any other study on intact menisci. This may be due to the strains being measured in 3D and in the center of the tissue. The highest strains occurred in the center of the tissue as opposed to the outer boundaries. 4 Higher strain values have been found when testing resected tissue. Tissakht et al. 16 performed elongation tests to failure on sections of tissue comparing the radial and circumferential strain. The failure strains for radial tests between different layers ranged from
20.82-60.62% whereas circumferential ranged from 17.15–34.1%. As the mean strains found in the current study are well below these reported failure strains, the results of the current study are corroborated by the previous research in this area.
The limitations of this study include the sample size of knees tested given the variability of the results.
However, in-vitro testing is both costly and time consuming, and this initial study of ten cadaveric knee 35
joints offers an initial baseline of the magnitude and distribution of strain in the native meniscus. There was also variability in the state of the meniscus of each knee; four had noticeable degeneration or tears in the tissue, and the average age of the specimens (67 years) represented an older population. There was also some variability in the location of the markers placed in the meniscus as the markers were placed manually using arthroscopy. However, efforts were made to ensure the markers were as equidistant as possible and tetrahedron volume was no greater than 9mm 3 to ensure the tissue contained within the tetrahedron can be assumed homogeneous. 19 The knee flexion angle of 5 degrees was set using a handheld goniometer which has been shown to have variability of only ±1.56°. 13
This method will be used to investigate differences in surgical interventions in future work. The repeatability testing illustrates that variability between repeated trails are small enough that changes due to surgical interventions may be detected.
2.6 Conclusion
A method of measuring 3D strain in an in-vitro cadaveric model has been presented. The strain measurements found in this study illustrate strains under normal physiological load in the range of 3-8%.
Strain measurements in the middle region of the meniscus were not found to be different from the posterior region at a knee flexion angle of 5 °.
Future work will evaluate the application of this technique to evaluate differences in knee position and between surgical fixation techniques for meniscal allograft transplants.
2.7 Acknowledgements
This study was supported by a research grant from the Musculoskeletal Transplant Foundation and by the
Joint Motion Program – A CIHR training program in musculoskeletal health research and leadership. 36
2.8 References
1. Amano, H., Iwahashi, T., Suzuki, T., Mae, T., Nakamura, N., Sugamoto, K., Shino, K., Yoshikawa, H., Nakata, K., 2015. Analysis of displacement and deformation of the medical meniscus with a horizontal tear using a three dimensional computer model. Knee. Surg. Sports. Traumatol. Arthrosc. 23(4), 1153-1160. 2. Chen, H., Yang, K., Dong, Q., Wang, Y., 2014. Assessment of tibial rotation and meniscal movement using kinematic magnetic resonance imaging. J. Orthop. Surg. Res. 9, 65-68. 3. Chen, L., Gordon, K.D., Hurtig, M., 2014. Design and validation of a cadaveric knee joint loading device compatible with magnetic resonance imaging and computed tomography. Med. Eng. Phys. 36(10), 1346-51. 4. Chia, H.N., Hull, M.L., 2007. Compressive Moduli of the Human Medial Meniscus in the Axial and Radial Directions at Equilibrium and at a Physiological Strain Rate. J. Orthop. Res. 26(7) Online. 5. Freutel, M., Seitz, A.M., Galbusera, F., Bornstedt, A., Rasche, V., Knothe, Tate. M.L., Ignatius, A., Durselen, L., 2015. Analysis of displacement and deformation of the medial meniscus with a horizontal tear using a three-dimensional computer model. Knee. Surg. Sports. Traumatol. Arthrosc. 23, 1153-1160. 6. Hutchinson, I.D., Moran, C.J., Potter, H.G., Warren, R.F., Rodeo, S.A., 2013. Restoration of the Meniscus Form and Function. Am. J. Sports. Med. 42-4. 7. Kessler, O., Sommers, M., Augustin, T., Haybaeck, J., D’Lima, D.D., Madey, S,M., Bottlang, M., 2015. Higher strains in the inner region of the meniscus indicate a potential source for degeneration. J. Biomech. ahead of print. 8. Lai, J.H., Levenston, M.E., 2010. Meniscus and Cartilage Exhibit Distinct Intra-Tissue Strain Distributions Under Unconfined Compression. Osteoarthr. Cartilage. 18(10), 1291-1299. 9. Lin, D.L., Ruh, S.S., Jones, H.L., Karim, A., Noble, P.C., McCulloch, P.C., 2013. Does High Knee Flexion Cause Separation of Meniscal Repairs? Am. J. Sports. Med. 41(9), 2143-2150. 10. MacLeod, T.D., Subburaj, K., Wu, S., Kumar, D., Wyatt, C., Souza, R.B., 2015. Magnetic resonance analysis of loaded meniscus deformation: a novel technique comparing participants with and without radiographic knee osteoarthritis. Skeletal. Radiol. 44(1), 125-35. 11. Makris, E.A., Hadidi, P., Athanasiou, K.A., 2011. The knee meniscus: Structure-function, pathophysiology, Current repair techniques and prospects for regeneration. Biomaterials. 32, 7411-7431. 12. Mastrokalos, D.S., Panayiotis, J., Papagelopoulos, J., Mavrogenis, A.F., Hantes, M.E., Paessler, H.H., 2008. Changes of the posterior meniscal horn height during loading: An in vivo magnetic resonance imaging study. Orthpedics. 31, 1. 13. Milanese, S., Gordon, S., Beuttner, P., Flavell, C., Ruston, S., Coe, D., O’Sullivan, W., McCormack, S., 2014. Reliability and concurrent validity of knee angle measurement: Smart phone app versus universal goniometer used by experienced and novice clinicians. Manual Therapy. 19(6), 569-574. 14. Seitz, A.M., Lubomierski, A., Friemert, B., Ignatius, A., Durselen, L., 2011. Effect of Partial Meniscectomy at the medial posterior horn on tibiofemoral contact mechanics and meniscal hoop strains in human knees. J. Orthop. Res. 30(6), 934-42. 37
15. Spencer Jones, R., Keene, G.C.R., Learmonth, D.J.A., Bickerstaff, D., Nawana, N.S., Costi, J.J., Pearcy, M.J., 1996. Direct Measurement of Hoop Strains in the Intact and Torn Human Medial Meniscus. Clin. Biomech . 11(5), 295-300. 16. Tissakht, M., Ahmed, A.M., 1995. Tensile Stress-Strain Characterics of the Human Meniscal Material. J. Biomechanics. 28(4), 411-422. 17. Vedi, V., Williams, A., Tennant, S.J., Spouse, E., Hunt, D.M., Gedroyc, W.M.W., 1999. Meniscal movement an in-vivo study using dynamic MRI. J. Bone. Joint. Surg. [Br] 81-B, 37-41. 18. Vrancken, A.C.T., Buma, P., van Tienen, T.G., 2013. Synthetic meniscus replacement: a review. International Orthopaedics. 37, 291-299. 19. Waldman, L.K., Fung, Y.C., Covell, J.W., 1985. Transmural Myocardial Deformation in the Canine Left Ventricle Normal in Vivo Three-Dimensional Finite Strains. Circ. Res. 57, 152-163. 20. Xu, C., Zhao, J., 2012. A meta-analysis comparing meniscal repair with meniscectomy in the treatment of meniscal tears: the more meniscus, the better outcome? Knee. Surg. Sports. Traumatol. Arthrosc. 23, 164-170.
38
Note: Chapter 3 is to be submitted for publication in a relevant clinical journal
3.0 Chapter 3: 3D Strain in Native Medial Meniscus Compared to Medial Meniscus Allograft Transplant
3.1 Abstract
This study presents a comparison of in-vitro three-dimensional strain in native meniscal tissue to strain in meniscal allograft transplants. Strain is calculated by tracking small teflon markers implanted within the meniscal tissue using computed tomography imaging of human cadaveric knees, under simulated physiologically relevant loading. Two surgical fixation techniques are evaluated; one using soft tissue anterior and posterior root fixation via transosseous suture and one using soft tissue anterior and posterior root fixation via transosseous suture with a 3rd peripheral transosseous suture fixation. Strain measurements for meniscal allograft transplants were found to replicate the range found within the native menisci and no significant differences in the distribution of strain were uncovered. In addition, no significant differences in the strain measurements were found between the two techniques of soft tissue fixation for the MAT. Measures of meniscal extrusion obtained from magnetic resonance images corroborated strain results. These results suggest that postoperative meniscal allograft transplants perform in a similar manner to the native meniscus, and that the addition of a peripheral anchor may not be necessary to replicate native tissue strain or improve the chondroprotective effect.
Keywords: Meniscus, strain, soft tissue biomechanics
3.2 Introduction
The menisci function to stabilize and distribute load through the joint as well as acting to reduce friction, increase lubrication, provide nutrients to the articular cartilage, and increase conformity between the 39
surfaces of the tibia and femur. 15 Meniscal injuries are one of the highest frequency injuries seen in orthopaedics. 4 This is a concern as injury or degeneration of the meniscus is a risk factor for the progression of osteoarthritis in the knee joint. Meniscus related surgeries are a common procedure; in the
USA alone there are over 1,000,000 meniscal related surgeries performed each year and that number continues to grow. 9
In the face of irreparable meniscal injury, treatment options include partial or total meniscectomy. A study by Baker et al.4 found that in the general population in the US, the incidence of meniscal injuries leading to meniscectomy was 61 in 100 000. Unfortunately, as noted by Fairbanks in 1948, meniscectomy causes deleterious effects to knee joint mechanics 7, resulting in pain and degeneration due to disruption of load distribution, increased cartilage contact stress and loss of stability. 6, 16 Studies have shown that total meniscectomy can produce a 14-fold increase in osteoarthritis. 9 This has led to a greater focus on studying meniscal function and the impact of meniscus loss, and increased investigation into repair and rehabilitative techniques to preserve meniscal function. 15, 22 It is essential that repair of the meniscus is attempted when possible, and meniscus replacement considered in applicable cases. 9, 15
Meniscal allograft transplantation (MAT) has been shown to reduce pain and help restore function for patients who are symptomatic following a full or partial meniscectomy. 6, 16 It has been shown that MAT does improve symptoms, function, and quality of life at 7-to-14 years of follow-up 23, however, there is still a question of the long term chondroprotective effect of MAT. 15
Currently, there is disparity in the surgical techniques used for MAT fixation, with three broad root fixation techniques involving the use of bone plugs, a bone bridge/slot and soft tissue only. To date, there is no consensus as to which technique produces the best results. 22 Cadaveric studies favour bony fixation over suture-only fixation to ensure tibial contact forces and hoop stresses are recreated as close as possible. 19 Clinical studies, however, do not corroborate these results and instead have shown both 40
methods to alleviate symptoms and produce good mid- to long-term results. 19 Overall, reviews of studies evaluating different methods have yet to determine which fixation technique is most efficacious. 15, 19, 22
Establishing which fixation methods ensure the best results could lead to improved outcomes for MAT, including provision of a greater chondroprotective effect.
This study evaluates two different methods of soft tissue fixation. Studies have reported positive clinical outcomes achieved through soft tissue fixation alone. 1, 3, 8, 16, 19, 23 It has been suggested that soft tissue fixation techniques may be superior to bone fixation techniques because soft tissue fixation causes less intra-articular damage and has the ability to be conducted fully arthroscopically. 3 As well, it has also been noted that the use of bone fixation requires a higher degree of accuracy in size matching of the allograft. Size matching is one of the crucial components of graft results so this may significantly affect the procedure. 15
A common complication related to MAT is extrusion of the allograft outside the boundaries of the tibial plateau. 15 Meniscal extrusion may compromise the function of the MAT and increase the risk of failure of the graft through degeneration or tears. 15 This is because extrusion reduces the contact area within the joint and causes an increase in stress due to the loss of load distribution and stability. 9 A measure of 3 mm past the edge of the tibial plateau is the usual threshold outside which meniscal extrusion is believed to be pathologic.1 However, this measurement can be subjective to whomever is performing the analysis. 1
It also varies based on the size of the menisci. Rating the amount of meniscal extrusion as a percent of meniscal body width may further standardize results. 1
It has also been found that the amount of meniscal extrusion post MAT surgery does not directly correlate with symptoms and functional improvement in the patient. 9 It has not been shown to have any adverse effect on clinical or functional outcomes (Lysholm score). 19, 22 Furthermore, studies have found that the 41
amount of meniscal extrusion did not increase over time post-surgery and may not lead to further extrusion or degeneration. 12, 14 Extrusion has also not been found to be linked to the method of fixating the MAT, however, it is still used as a comparative measure for chondroprotective effect. 10
Due to the lack of consensus on the use of meniscal extrusion as on outcome measure, a more objective standardized method of evaluation is required. This study attempts to evaluate the post-operative efficacy of transplanted medial menisci, with and without an additional peripheral 3 rd point of fixation on the tibial plateau by comparing strain in the tissue as well as the degree of postoperative meniscal extrusion.
3.3 Methods
This controlled laboratory study was performed following local institutional review board approval. Ten fresh frozen human cadaveric knees (5 male, mean age 67) were evaluated using a novel loading device which is capable of applying repeatable positioning and loading of a human cadaveric knee joint using simulated quadriceps and hamstrings muscle forces. The loading device is capable of applying repeatable positioning and loading of a human cadaveric knee joint. 5 Specimens were prepared for imaging as outlined below, then positioned and micro computed tomography (CT) and magnetic resonance (MR) images were acquired with and without a simulated muscle load applied.
3.3.1 Specimen Preparation
The cadaveric knees were first prepared as outlined in a previous publication to enable insertion in the loading device. 5 Eight 0.8 mm diameter teflon beads were then inserted in two tetrahedral formations in the middle 1/3 and posterior 1/3 of the native medial meniscus under arthroscopic guidance using an 18 gauge spinal needle. The knee was then manually manipulated through ten cycles of flexion and extension prior to testing. The joint was mounted into the loading device and the flexion angle was set using a hand- 42
held goniometer. The flexion angle was set at 5° for CT and both 5° and 30° for MR. The CT could not accommodate flexion angles higher than 5° due to the smaller bore size.
3.3.2 MAT Procedure
Meniscal allografts were sourced from the Musculoskeletal Transplant Foundation (MTF) and size matched to the study knees using fluoroscopic tibial plateau coronal width measurements with magnification marker as per the Pollard method. 20 Eight markers (0.8 mm teflon beads) were inserted in two tetrahedral formations in the middle 1/3 and posterior 1/3 of the medial meniscus allograft using an
18 gauge spinal needle. The native medial meniscus was then removed arthroscopically and replaced with a meniscus allograft utilizing soft tissue anterior and posterior root fixation with trans osseous sutures tied over an anterolateral proximal tibial cortical bone bridge (Figure 1). A further 3 rd trans osseous tunnel was fashioned with a suture applied to the 50% position of the meniscus circumference tied over a button on the anterolateral proximal tibia providing a peripheral fixation on the tibial plateau. 24 The button allowed the suture to be easily cut or tied so both surgical fixation methods could be tested in a randomized order.
This three tunnel technique is described in Stone et al. 24
Figure 3.1: This diagram depicts the three tunnel surgical fixation technique, first illustrating the placement of the three tunnels, the insertion of the MAT and where the sutures are tied. 24 43
3.3.3 Imaging
CT imaging was acquired using a 154 µm resolution volumetric cone-beam micro-CT scanner (GE Locus
Ultra) with an approximately 16 second image acquisition time. The specimen was imaged first without any applied load, following which load was applied to the knee joint via the quadriceps and hamstrings muscle cables until a joint load of approximately 1 x body weight (650±160 N) was reached. Another image was then acquired in the loaded state. MR imaging was also acquired using a 3T Prisma MRI D13, with a resolution of 0.45 by 0.45 mm by 0.8 mm slice thickness and approximately 6 minute acquisition time. The same process was repeated as in CT (acquisition of an unloaded and loaded image) but with the additional flexion angle of 30° obtained. The 30° angle was chosen as a clinically relevant flexion angle.
Flexion angles greater than 5 degrees were not evaluated in the CT due to the size of the bore of the GE
Locus Ultra, which did not accommodate the flexed knee.
The imaging process for both CT and MR was then repeated for the knee following MAT, with randomized order either with the 3 rd peripheral suture tied then followed by the suture being cut or without the 3 rd peripheral suture tied then having it tied.
3.3.4 Analysis
To quantify the strain in the tissue, the centroid 3D coordinates of each marker were recorded using
MicroView 3D Image Viewer 2.5.0. To create a tibial coordinate system, anatomical landmarks were chosen from each image. These landmarks were visually approximated as the center of the medial and lateral femoral contact areas on the tibial plateau and the center most distal point on the tibia. The line from the lateral to medial landmark is the medial-lateral axis (positive medial) and the mid-point between those two points to the distal landmark is the superior-inferior axis (positive superior). A cross product of the medial lateral and inferior superior axes was performed to generate the anterior-posterior axis. Then a second cross product of the superior-inferior and anterior-posterior axes was taken to form a new medial- 44
lateral axis, creating an anatomical coordinate system (See Appendix 1) with three orthogonal axes.
Marker coordinates were then transformed into this tibial coordinate system to establish anatomical directions for calculations of strain. These coordinates were then input into a custom written program
(Matlab R2014a, The MathWorks Inc.) to calculate the three dimensional strain from the unloaded and loaded marker positions as described by Waldman et al. 26 The markers that formed the vertices of the tetrahedron were non-coplanar and defined a volume no greater than 9 mm 3 and no less than 0.1 mm 3.
Preliminary results showed this to be a reasonable range of volume measurements, above or below which the strain results became erratic. The tetrahedron must be small enough that the tissue properties can be assumed to be homogeneous throughout. 26
Six independent strains were obtained, three principal strains and three shearing strains, according to
Equation 1.
∆ − ∆ = 2 ∆ ∆ (1)
Where ∆so is the original distance between the markers prior to loading and ∆s is the distance between the markers after loading, E is the strain, ∆ai is the distance from the first marker to the tibial coordinate
26 system and ∆aj is the distance from the second marker to the tibial coordinate system. This equation yields six algebraic equations which can be solved to obtain the six strain components of the symmetric strain tensor.
Meniscal extrusion was measured in the coronal plane using the technique described by Lee et al. 13 using
OsiriX Imaging Software (open source software). Since maximal graft extrusion in the coronal plane usually occurs at the mid-body region, extrusion was measured on the most central slice. Absolute meniscal extrusion, defined as the distance between the outer edge of the tibial plateau and the outer edge of the meniscus, was measured. Relative percentage of extrusion (RPE), defined as the width of the extruded menisci relative to the total width of the meniscus, was then calculated. The extrusion 45
measurements were performed by two trained surgeons and averaged for each knee and each surgical condition.
3.3.5 Statistical Analysis
Statistical analysis using repeated measures ANOVA (IBM SPSS Statistics 22) was conducted to determine differences in strain between intact menisci, allograft menisci with the 3 rd peripheral suture and allograft menisci without the 3 rd peripheral suture. For extrusion measurements, statistical analysis using a paired t-test was conducted to determine differences between allograft menisci with the 3 rd peripheral suture and allograft menisci without the 3 rd peripheral suture.
3.4 Results
Figure 2 shows the average 3D strain found in eight knees for the middle 1/3 of the meniscus for all three conditions. Figure 3 shows the average 3D strain found in eight knees for the posterior 1/3 of the meniscus for all three conditions. Medial-Lateral (ML), Anterior-Posterior (AP) and Superior-Inferior
(SI) principal strains are shown. Directions ML/AP, ML/SI and AP/SI indicate shearing strains. Figure 4 shows the average percent extrusion of the MAT at 5° and 30° of flexion for both surgical conditions.
Figure 5 shows the average linear extrusion of the MAT at 5° and 30° of flexion for both surgical conditions. 46
Figure 3.2: Average strain profile measured from the middle tetrahedron (N=8). Strains are shown for each principal direction medial-lateral (ML), anterior-posterior (AP) and superior-inferior (SI) and shearing strains (ML-AP, ML-SI, AP-SI). A) Intact meniscus B) MAT using soft tissue anterior and posterior root fixation via transosseous suture C) MAT using soft tissue anterior and posterior root fixation via transosseous suture with a 3rd peripheral transosseous suture fixation. Errors bars represent standard deviations.
Figure 3.3: Average strain profile measured from the posterior tetrahedron (N=8). Strains are shown for each principal direction medial-lateral (ML), anterior-posterior (AP) and superior-inferior (SI) and shearing strains (ML-AP, ML-SI, AP-SI). A) Intact meniscus B) MAT using soft tissue anterior and posterior root fixation via transosseous suture C) MAT using soft tissue anterior and posterior root fixation via transosseous suture with a 3 rd peripheral transosseous suture fixation. Errors bars represent standard deviations. 47
No statistically significant difference was found between the middle and posterior strains in the intact knee compared to the meniscus allograft, either with or without the 3 rd peripheral suture fixation, with an observed power of 33.2%.
Figure 3.4: Average percent extrusion plus/minus standard deviation found for the MAT with each surgical technique (N=11) A) MAT using soft tissue anterior and posterior root fixation via transosseous suture and B) MAT using soft tissue anterior and posterior root fixation via transosseous suture with a 3 rd peripheral transosseous suture fixation.
Figure 3.5: Average linear extrusion plus/minus standard deviation found for the MAT with each surgical technique (N=11) A) MAT using soft tissue anterior and posterior root fixation via transosseous suture and B) MAT using soft tissue anterior and posterior root fixation via transosseous suture with a 3 rd peripheral transosseous suture fixation.
48
No statistically significant difference was found regarding the degree of extrusion in the meniscus allograft, either with or without the 3 rd peripheral suture fixation, with an observed power of 41.6% for 5° and 43.8% for 30°.
3.5 Discussion
The most important finding of this study is that at time zero, current soft tissue fixation techniques of
MAT result in similar principal and shear strain values to that of native menisci. This result was corroborated with extrusion measurements, a commonly cited outcome measure for chondroprotective effect, 10 which also indicated no difference between the two soft tissue fixation techniques., Additional peripheral fixation did not seem to have an impact on either strain measurement or meniscal extrusion measurement in this model. These results, and the similarities in the strain distributions between intact and medial MAT, in both surgical conditions, are corroborated by other research showing positive outcomes with soft tissue fixation alone. 1, 3, 8, 16, 23
To the authors’ knowledge, this is the first study to quantitatively study regional 3D meniscal strain in human knees under simulated physiological loading with the purpose of evaluating differences between native menisci and MAT. This could lead to a more standardized method of comparison to elucidate the efficacy of different surgical fixation techniques for MAT, as well as for the development of meniscal prostheses or scaffolds.
The strain results for the MAT, especially for the middle tetrahedral position, seem to follow the same pattern as the intact meniscus in which the meniscus responds and deforms in response to tibiofemoral loading (Figure 2). Tibiofemoral loading causes hoop stresses in the meniscus, 16 which may result in fibres in the ML direction being compressed and fibres in the AP direction being tensioned as the meniscus is mainly anchored at the anterior and posterior horn attachments. The tensile strain in the 49
middle region of the meniscus in the SI direction is accompanied by the compressive strain in the ML direction. In the posterior region of the meniscus, the SI direction strains show larger differences between the intact meniscus (approximately -6%) and MAT with soft tissue anterior and posterior root fixation via transosseous suture (approximately -3%) and MAT using soft tissue anterior and posterior root fixation via transosseous suture with a 3rd peripheral transosseous suture fixation (approximately +3%) (Figure
3). It could be that the additional peripheral suture, which creates an additional fixation point on the medial edge of the meniscus, is creating the observed tensile SI strain in the posterior of the meniscus.
Standard deviations, however, are too large to be significant.
The extrusion results illustrate a couple of interesting conclusions, despite the lack of significant findings
(Figure 3). The first observation is that extrusion measurements are, as expected, larger when the knee is loaded compared to unloaded. There is also a trend towards higher extrusion when the knee is flexed to the thirty degree position compared to full extension. This may be a clinically important finding that warrants further investigation. Finally, when comparing the two surgical fixation techniques, there is a trend towards a lower value of extrusion for fixation with a third peripheral fixation point compared to no third anchor. This intuitively makes sense since that third peripheral point is placed at approximately the same anatomical location as the coronal slice where the extrusion measurement is made. This result suggests that extrusion of the MAT is decreased by the addition of this third anchor point.
Finally, a relation between the extrusion measurements and the strain in the middle tetrahedron is expected given the nature of these two measurements. However, after comparison of these quantities no relationship is apparent. This is due to the relatively small number of subjects (only seven knees were available that had both middle strain and extrusion measurements), the subjective nature of the extrusion measurement, and the relatively high standard deviations for both measurements.
50
A similar study, using human cadaveric knee joints, assessed the need for circumferential fixation of the
MAT by evaluating the fixation of the native meniscus to the joint capsule and medial collateral ligament. 25 This was accomplished by analyzing the movement of, firstly, the intact medial meniscus, then the meniscus with circumferential fixation to the joint capsule and collateral ligament cut, and lastly with rim of the meniscus reattached with sutures to the periphery. This analysis was completed with a 6 degree of freedom loading similar to a squat position to a maximum load of 1000N. This study did not find any significant difference in the joint kinematics under load with and without circumferential fixation. This study further highlights that the main anchoring of the meniscus is by the horn attachments.
The limitations of this study include the sample size of knees tested given the variability of the results.
However, in-vitro testing is both costly and time consuming, and this initial study of nine cadaveric knee joints offers an initial baseline of the magnitude and distribution of strain in both the intact meniscus and the MAT. There was also variability in the state of the intact meniscus of each knee; four of the nine knees had noticeable deterioration or tears in the tissue, and the average age of the specimens (67 years) represented an older population. There was also some variability in the location of the markers placed in the meniscus and MAT as the markers were placed manually using arthroscopy. However, efforts were made to ensure the markers were as equidistant as possible and tetrahedron volume was no greater than 9 mm 3 to ensure the tissue contained within the tetrahedron can be assumed homogeneous. 26 The knee flexion angle of 5 degrees was set using a handheld goniometer which has been shown to have variability of only ±1.56°. 18
More testing is required to validate these results and assess differences in strain between these two fixation techniques. The efficacy of the additional peripheral fixation point described may require a cyclic loading protocol to uncover any mechanical advantages.
51
3.6 Conclusion
A new method of measuring of 3D strain in an in-vitro cadaveric model is presented which can be used to compare differences in surgical fixation techniques for MAT. Strain measurements for medial MAT were found to replicate the range found within the native menisci and no significant differences in the distribution of strain were uncovered. These results suggest that time zero MAT performs in a similar manner to the native meniscus, and that the addition of a peripheral anchor in medial MAT may not be necessary to replicate native tissue strain or improve the chondroprotective effect of MAT at time zero.
Measurements of extrusion of the MAT also found no significant difference between the two surgical techniques which supports this finding. It is unclear what effects cyclic loading over time would have on this model in an in-vivo environment.
3.7 Acknowledgements
This study was supported by a research grant from the Musculoskeletal Transplant Foundation and by the
Joint Motion Program – A CIHR training program in musculoskeletal health research and leadership. 52
3.7 References
1. Abat, F., Gelber, P.E., Erquicia, J.I., Tey, M., Gonzalez-Lucena, G., Monllau, J.C., 2013. Prospective comparative study between two different fixation techniques in meniscal allograft transplantation. Knee. Surg. Sports. Traumatol. Arthrosc. 7, 1516-1522. 2. Abat, F., Gelber, P.E., Erquicia, J.I., Pelfort, X., Gonzalez-Lucena, G., Monllau, J.C., 2012. Suture-Only Fixation Technique Leads to a Higher Degree of Extrusion Than Bony Fixation in Meniscal Allograft Transplantation. Am. J. Sports. Med. 40, 1591-1596. 3. Alentorn-Geli, E., Vazquez, R.S., Balletbo, M.G., Diaz, P.A., Steinbacher, G., Segarra, X.C., Vilarrubia, M.R., Bertameu, R.C., 2011. Arthroscopic meniscal allograft transplantation without bone plugs. Knee. Surg. Sports. Traumatol. Arthrosc. 19, 174-182. 4. Baker, B.E., Peckham, A.C., Pupparo, F., Sanborn, J.C., 1985. Review of Meniscal Injury and Associated Sports. Am. J. Sports. Med. 13(1), 1-4. 5. Chen, L., Gordon, K.D., Hurtig, M., 2014. Design and validation of a cadaveric knee joint loading device compatible with magnetic resonance imaging and computed tomography. Med. Eng. Phys. 36(10), 1346-51. 6. De Coninck, T., Huysse, W., Verdonk, R., Verstraete, K., Verdonk, P., 2013. Open Versus Arthroscopic Meniscus Allograft Transplantation: Magnetic Resonance Imaging Study of Meniscal Radial Displacement. Arthroscopy. 29(3), 514-521. 7. Fairbank, T.J., 1948. Knee Joint Changes After Meniscectomy. J. Bone. Joint. Surg. 30b(4), 664- 670. 8. Gonza´ lez-Lucena, G., Gelber, P.E., Pelfort, X., Tey, M., Monllau, J.C., 2010. Meniscal allograft transplantation without bone blocks: a 5- to 8-year follow-up of 33 patients. Arthroscopy. 26(12), 1633-1640. 9. Ha, J.K., Shim, J.C., Kim, D.W., Lee, S.K., Ra, H.J., Kim, J.G., 2010. Relationship Between Meniscal Extrusion and Various Clinical Findings After Meniscus Allograft Transplantation. Am. J. Sports. Med. 38, 2448. 10. Koh YG, Moon HK, Kim YC, Park YS, Jo SB, Kwon SK. Comparison of medical and lateral meniscal transplantation with regard to extrusion of the allograft, and its correlation with clinical outcome. J Bone Joint Surg Br 2012;94-B:190-3. 11. Lee, B.S., Kim, J.M., Kim, K.A., Bin, S.I., 2015. Patient-Related Risk Factors for the Extrusion of Lateral Meniscal Allograft Transplants. Arthroscopy. 31(4), 699-706. 12. Lee DH, Kim TH, Lee SH, Kim CW, Kim JM, Bin S. Evaluation of meniscus allograft transplantation with serial magnetic resonance imaging during the first postoperative year: focus on graft extrusion. Arthroscopy 2008;24:1115–1121 13. Lee, D.H., Lee, C.R., Jeon, J.H., Kim, K.A., Bin, S.I. 2015. Graft Extrusion in Both the Coronal and Sagittal Planes Is Greater After Medial Compared With Lateral Meniscus Allograft Transplantation but Is Unrelated to Early Clinical Outcomes. The American journal of sports medicine. 43(1):213-219. 14. Lee JJ, Choi CJ, Choi YJ, Choi CH. Magnetic Resonance Imaging Evidence of Meniscal Extrusion in Medial Meniscus Posterior Root Tear. Arthroscopy 2010;26-12:1602-1606. 15. Lubowitz, J.H., Verdonk, P.C.M., Reid, J.B., Verdonk, R., 2007. Meniscus allograft transplantation: a current concepts review. Knee. Surg. Sports. Traumatol. Arthrosc. 15, 476-492. 53
16. Makris, E.A., Hadidi, P., Athanasiou, K.A., 2011. The knee meniscus: Structure-function, pathophysiology, Current repair techniques and prospects for regeneration. Biomaterials. 32, 7411-7431. 17. Marcacci, M., Zaffagnini, S., Muccioli, G.M.M., Grassi, A., Bonanzinga, T., Nitri, M., Bondi, A., Molinari, M., Rimondi, E., 2012. Meniscal Allograft Transplantation Without Bone Plugs : A 3- Year Minimum Follow-up Study. Am. J. Sports. Med. 40, 395. 18. Milanese, S., Gordon, S., Beuttner, P., Flavell, C., Ruston, S., Coe, D., O’Sullivan, W., McCormack, S., 2014. Reliability and concurrent validity of knee angle measurement: Smart phone app versus universal goniometer used by experienced and novice clinicians. Manual Therapy 19(6), 569-574. 19. Myers, P., Tudor, F., 2015. Meniscal Allograft Transplantation: How Should We Be Doing It? A Systematic Review. Arthroscopy. 31(5), 911-925. 20. Oh, K.J., Sobti, A.S., Yoon, J.R., Ko, Y.B., 2015. Current status of second-look arthroscopy after meniscal allograft transplantation: review of the literature. Arch. Orthop. Trauma. Surg. PMID: 26142541. 21. Pollard, M.E., Kang, Q., Berg, E.E., 1995. Radiographic Sizing for Meniscal Transplantation. Arthroscopy. 11(6), 684-687. 22. Samitier, G., Alentorn-Geli, E., Taylor, D.C., Rill, B., Lock, T., Moutzouros, V., Kolowich, P., 2015. Meniscal allograft transplantation. Part 1: systematic review of graft biology, graft shrinkage, graft extrusion, graft sizing, and graft fixation. Knee. Surg. Sports. Traumatol. Arthrosc. 23, 310-322. 23. Samitier, G., Alentorn-Geli, E., Taylor, D.C., Rill, B., Lock, T., Moutzouros, V., Kolowich, P., 2015. Meniscal allograft transplantation. Part 2: systematic review of transplant timing, outcomes, return to competition, associated procedures, and prevention of osteoarthritis. Knee. Surg. Sports. Traumatol. Arthrosc. 23, 323-333. 24. Stone, K.R., Walgenbach, A.W., 2003. Meniscal allografting: the three-tunnel technique. Arthroscopy . 19(4), 426-430. 25. Vrancken, A.C.T., van Tienen, T.G., Hannink, G., Janssen, D., Verdonschot, N., Buma, P., 2014. Releasing the circumferential fixation of the medial meniscus does not affect its kinematics. The Knee. 21, 1033-1038. 26. Waldman, L.K., Fung, Y.C., Covell, J.W., 1985. Transmural Myocardial Deformation in the Canine Left Ventricle Normal in Vivo Three-Dimensional Finite Strains. Circ. Res. 57, 152-163.
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4.0 Chapter 4: Conclusions and Recommendations
The primary goal of this research was to evaluate a new technique for measuring 3D strain in soft tissue, specifically the meniscus of the knee. Principal and shearing strains were evaluated in the middle third and posterior third of the meniscus. Additionally, this method was then used to determine if there are measurable changes in strain in the native menisci compared to transplanted tissue using two different surgical techniques.
This is the first study to quantitatively study regional 3D meniscal strain in a large number of human knees under simulated physiological loading. Determining the strain in the meniscus could help in evaluating properties necessary for synthetic implants, provide a quantitative measure to outline the onset of disease and evaluate rehabilitation recommendations to improve and standardize procedures. 4, 5 The strain measurements found in this study illustrate strains under normal physiological in the range of 3-8%.
Strain measurements in the middle region of the meniscus were not found to be different from the posterior region at a knee flexion angle of 5 degrees. Additional testing may uncover differences in direction of strain. The repeatability testing illustrates that variability between repeated trails are small enough that changes due to surgical interventions may be detected.
Knowledge of the 3D meniscal strain could provide an important quantitative measure for comparing outcomes for MAT. This would be beneficial as, currently, extrusion is used as a comparative measure for chondroprotective effect despite the fact that it has not been linked to surgical fixation technique. 1 In addition, although extrusion of the graft outside the tibial plateau is a common complication of MAT, it has not been proven to have any adverse effect on clinical or functional outcomes (Lysholm score). 7, 8
55
There is a gap in literature concerning proper fixation techniques; no consensus has been reached as to which surgical fixation techniques produce the best results. 7 Soft tissue fixation has produced positive results and causes less damage to the articular cartilage and is therefore a promising technique to study. 1
The results of this study do not indicate a significant difference in strain between the native meniscus and a MAT with and without an additional peripheral anchor. The MAT appears to replicate the intact strain distribution. These results suggest that a peripheral anchor in medial MAT may not be necessary to replicate native tissue strain or improve the chondroprotective effect of MAT at time zero.
More testing is required to validate these results and assess differences in strain between these two fixation techniques. The efficacy of the additional peripheral fixation point described may require a cyclic loading protocol to uncover any mechanical advantages. This method could be used to investigate differences in other surgical interventions in future work.
The limitations of this study include firstly, the sample size of knees tested given the variability of the results. However, this does offer an initial baseline of the magnitude and distribution of strain in the native meniscus and MAT. There was also variability in the health of the meniscus of each knee, 4 of the
10 knees had noticeable degeneration and/or tears in the tissue. Degeneration may cause the strain values to be increased compared to healthy tissue. The average age of the specimens (67 years) represented an older population which may also cause the strain results to be increased compared to a younger population.
There was some variability in the location of the markers placed in the meniscus as the markers were placed manually using arthroscopy. However efforts were made to ensure the markers were as equidistant as possible and tetrahedron volume was no greater than 9 mm 3 to ensure the tissue contained within the tetrahedron can be assumed homogeneous. 10 The coordinates chosen to represent these 56
markers were chosen by zooming in on the marker using MicroView 3D Image Viewer 2.5.0 and choosing the point closest to the center. This could also be completed using region grow but could be more time consuming to run. The maximum standard deviation in strain results found over ten trials on the same knee for each of these methods of determining coordinates was 1.42%.
The method of preparing the knee joint involves drilling holes through the tibia to place the cables for the simulated muscle pull of the quadriceps and hamstrings. The exact placement of these holes and therefore the exact location and angle of pull will vary slightly with each knee.
The knee flexion angle of 5 degrees was set using a handheld goniometer which has been shown to have variability of only ±1.56°. 6 The loading was applied using the device described in Chen et al. 2 There is some inherent variability in loading this device. For this study a standard deviation of ±160 N was found for a target load of 650 N.
There is also some variability in the method of choosing coordinates from the CT scans to create the tibial coordinate system as this is done manually. A series of five trials of point picking the landmarks off the
CT image was completed to evaluate the repeatability of this method. A maximum standard deviation from these five trials was 1.18 mm.
Future work will involve improvements to the testing method and device itself. For the testing method, markers need to be placed on the tibia and femur to create coordinate systems. This makes the data more objective. Although this was completed for this study, the data was not used because the error was too high. This could be corrected by changing the placement of the markers (0.8mm, Teflon beads). In this study, the markers were placed about 1 cm apart due to the space constraints created by the CT imaging length (9 cm). Due to the proximity of the markers, small errors in digitizing created larger errors in the angle of the coordinate system. As well, it was difficult to determine which marker was which in the CT 57
image compared to what was digitized. In future testing, placement of the markers could be evaluated to determine if there is somewhere else where the markers can be drilled into the bone within the 9 cm that does not disrupt the joint capsule but allows for larger spacing in between the markers. As well, different types of metal or sizes of beads could be used to differentiate between markers.
Future work should also involve cyclic loading of the knee joint which may help uncover differences in surgical fixation technique that are not revealed in single loading and unloading cycles. This would involve updating the programming to set unloading and loading regimes and testing to ensure that repeatability is still accurate.
Further testing could also potentially involve testing at higher flexion angles which may uncover differences in strain in the middle and posterior. This is due to higher strain found in the posterior at higher flexion angles. 8 The device currently reaches a maximum flexion angle of approximately 70°.
The device could potentially reach much higher flexion angles if longer cadaveric joints could be used i.e. less of the tibia and femur removed; however, steps would need to be taken to ensure proper angles of pull on the cables. Possibly through additional brass eye screws screwed into the bone. The CT, unfortunately only fits a maximum angle of approximately 10° flexion so these tests would need to be done in MRI. Although the Teflon markers do show up as a void in the MRI, there could be more error in finding the centroids of the markers.
58
4.1 References
1. Alentorn-Geli, E., Vazquez, R.S., Balletbo, M.G., Diaz, P.A., Steinbacher, G., Segarra, X.C., Vilarrubia, M.R., Bertameu, R.C., 2011. Arthroscopic meniscal allograft transplantation without bone plugs. Knee. Surg. Sports. Traumatol. Arthrosc. 19, 174-182. 2. Chen, L., Gordon, K.D., Hurtig, M., 2014. Design and validation of a cadaveric knee joint loading device compatible with magnetic resonance imaging and computed tomography. Med. Eng. Phys. 36(10), 1346-51. 3. Koh, Y.G., Moon, H.K., Kim, Y.C., Park, Y.S., Jo, S.B., Kwon, S.K., 2012. Comparison of medical and lateral meniscal transplantation with regard to extrusion of the allograft, and its correlation with clinical outcome. J. Bone. Joint. Surg. Br. 94-B, 190-3. 4. Lai, J.H., Levenston, M.E., 2010. Meniscus and Cartilage Exhibit Distinct Intra-Tissue Strain Distributions Under Unconfined Compression. Osteoarthr. Cartilage. 18-10, 1291-1299. 5. MacLeod, T.D., Subburaj, K., Wu, S., Kumar, D., Wyatt, C., Souza, R.B., 2015. Magnetic resonance analysis of loaded meniscus deformation: a novel technique comparing participants with and without radiographic knee osteoarthritis. Skeletal Radiol. 44-1, 125-35. 6. Milanese, S., Gordon, S., Beuttner, P., Flavell, C., Ruston, S., Coe, D., O’Sullivan, W., McCormack, S., 2014. Reliability and concurrent validity of knee angle measurement: Smart phone app versus universal goniometer used by experienced and novice clinicians. Manual Therapy. 19(6), 569-574. 7. Myers, P., Tudor, F., 2015. Meniscal Allograft Transplantation: How Should We Be Doing It? A Systematic Review. Arthroscopy. 31(5), 911-925. 8. Samitier, G., Alentorn-Geli, E., Taylor, D.C., Rill, B., Lock, T., Moutzouros, V., Kolowich, P., 2015. Meniscal allograft transplantation. Part 1: systematic review of graft biology, graft shrinkage, graft extrusion, graft sizing, and graft fixation. Knee. Surg. Sports. Traumatol. Arthrosc. 23, 310-322. 9. Spencer Jones, R., Keene, G.C.R., Learmonth, D.J.A., Bickerstaff, D., Nawana, N.S., Costi, J.J., Pearcy, M.J., 1996. Direct Measurement of Hoop Strains in the Intact and Torn Human Medial Meniscus. Clin. Biomech . 11-5, 295-300. 10. Waldman, L.K., Fung, Y.C., Covell, J.W., 1985. Transmural Myocardial Deformation in the Canine Left Ventricle Normal in Vivo Three-Dimensional Finite Strains. Circ. Res. 57, 152-163.
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5.0 Appendix A
5.1 Determining the Tibial Coordinate System and Calculating Strain
To find the bony landmarks to create the tibial coordinate system, first the center slice of the coronal view of the knee was found (Figure 1). On the corresponding sagittal view (Figure 2) the coronal slice was moved to the middle of the anteroposterior distance of the tibial plateau. On that coronal slice, the center of the femoral contact area for the medial side was chosen (Figure 3). Then the center of the femoral contact area for the lateral side was chosen (Figure 4). On the corresponding sagittal view, the middle of the anteroposterior distance of the tibial plateau was found for that lateral side and the coronal slice was adjusted to that point. Then the lateral point was chosen. The distal point was chosen as the center point on the most distal transverse image slice (Figure 5).
Figure A.1: Coronal view center
Figure A.2: Sagittal view tibial center 60
Figure A.3: Medial point – femoral contact center
Figure A.4: Lateral point femoral contact center
Figure A.5: Distal center
To calculate the tibial coordinate system and strain the following code was used.
% Coordinates are chosen from the CT image % bd is the distal point % bm is the medial point % bl is the lateral point
% CT bony landmarks Unloaded CTdata = [68.2 113.9 3 103.8 125.4 31.5 59.9 112.6 39 ]; 61
bd=CTdata(1,:); bm=CTdata(2,:); bl=CTdata(3,:);
% CT bony landmarks Loaded CTdatal = [68.4 110.3 3 103.1 124.7 31.9 50.5 110.2 73.4 ]; bdl=CTdatal(1,:); bml=CTdatal(2,:); bll=CTdatal(3,:);
%The medial point bm to the lateral point bl forms the x axis (positive %medial) %The middle point between bm and bl to the distal point bz forms the y axis %(postive superior)
% Unloaded Landmark rotation bxo = bm - bl; mp = ((bm + bl)/2); bz = mp - bd;
%Taking the cross product of the x and y axis provides a third perpendicualar z axis %Then the cross product of the y and z axis is taken to get a new x axis - %This ensures that the axes are orthogonal
%%% Left Knee by = cross(bz, bxo); bx = cross(by, bz);
% %%% Right Knee % by = cross(bxo, bz); % bx = cross(bz, by);
%Normalizing each axes makes them all unit length
Bx = bx/norm(bx); By = by/norm(by); Bz = bz/norm(bz);
%Rb is the rotation matrix of the three normalized orthogonal vectors
Rb = [Bx; By; Bz];
% Tb is the transformation matrix built from the rotational matrix R and % the origin point (mp, the mid point between the medial and lateral points)
Tb = zeros(4,4); Tb(4,4) = 1; Tb(1:3,1:3) = Rb; 62
Tb(1:3,4) = mp;
%This section is the same calculation as the unloaded calculation, skip to %original bead positions
% Loaded Landmark rotation bxol = bml - bll; mpl = ((bml + bll)/2); bzl = mpl - bdl;
%%% Left Knee byl = cross(bzl, bxol); bxl = cross(byl, bzl);
% %%% Right Knee % byl = cross(bxol, bzl); % bxl = cross(bzl, byl);
Bxl = bxl/norm(bxl); Byl = byl/norm(byl); Bzl = bzl/norm(bzl);
Rbl = [Bxl; Byl; Bzl];
Tbl = zeros(4,4); Tbl(4,4) = 1; Tbl(1:3,1:3) = Rbl; Tbl(1:3,4) = mpl;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%% %%&
%Original bead positions %This is the position of the beads within the meniscal tissue in the %unloaded knee data3 = [114.24 126.19 33.35 113.03 123.11 33.45 116.22 122.34 35.16 113.59 121.41 34.02 ]; B1o=data3(1,:); B2o=data3(2,:); B3o=data3(3,:); B4o=data3(4,:);
%new unloaded bead positions %The position of the beads are transformed into the tibial coordinate system (rotated and translated to match %the position of the tibial coordinate system) 63
B1o = inv(Tb)*[B1o 1]'; B2o = inv(Tb)*[B2o 1]'; B3o = inv(Tb)*[B3o 1]'; B4o = inv(Tb)*[B4o 1]';
% %Bead positions after loading %This is the position of the beads within the meniscal tissue in the %loaded knee data4 = [114.61 125.42 33.44 113.42 122.49 33.58 116.75 121.72 35.38 114.1 120.65 34.26 ]; B1 = data4(1,:); B2 = data4(2,:); B3 = data4(3,:); B4 = data4(4,:);
%new loaded bead positions %transformed into the loaded tibial coordinate system B1 = inv(Tbl)*[B1 1]'; B2 = inv(Tbl)*[B2 1]'; B3 = inv(Tbl)*[B3 1]'; B4 = inv(Tbl)*[B4 1]';
%Distance between the beads (original and loaded) S12o=norm(B1o-B2o); S12=norm(B1-B2); S13o=norm(B1o-B3o); S13=norm(B1-B3); S14o=norm(B1o-B4o); S14=norm(B1-B4); S23o=norm(B2o-B3o); S23=norm(B2-B3); S24o=norm(B2o-B4o); S24=norm(B2-B4); S34o=norm(B3o-B4o); S34=norm(B3-B4);
%Unloaded % x, y, z distances between the beads %Bead 1 and 2 A1 = B1o(1) - B2o(1); A2 = B1o(2) - B2o(2); A3 = B1o(3) - B2o(3);
%Bead 1 and 3 A4 = B1o(1) - B3o(1); A5 = B1o(2) - B3o(2); A6 = B1o(3) - B3o(3);
64
%Bead 1 and 3 A7 = B1o(1) - B4o(1); A8 = B1o(2) - B4o(2); A9 = B1o(3) - B4o(3);
%Bead 1 and 3 A10 = B2o(1) - B3o(1); A11 = B2o(2) - B3o(2); A12 = B2o(3) - B3o(3);
%Bead 1 and 3 A13 = B2o(1) - B4o(1); A14 = B2o(2) - B4o(2); A15 = B2o(3) - B4o(3);
%Bead 1 and 3 A16 = B3o(1) - B4o(1); A17 = B3o(2) - B4o(2); A18 = B3o(3) - B4o(3);
%Calculation adapted from Waldman et. al 1985 "Transmural myocardial deformation %canine left ventrical
A=2*[A1^2 A2^2 A3^2 2*A1*A2 2*A1*A3 2*A2*A3;... A4^2 A5^2 A6^2 2*A4*A5 2*A4*A6 2*A5*A6;... A7^2 A8^2 A9^2 2*A7*A8 2*A7*A9 2*A8*A9;... A10^2 A11^2 A12^2 2*A10*A11 2*A10*A12 2*A11*A12; ... A13^2 A14^2 A15^2 2*A13*A14 2*A13*A15 2*A14*A15; ... A16^2 A17^2 A18^2 2*A16*A17 2*A16*A18 2*A17*A18];
b=[S12^2-S12o^2; S13^2-S13o^2; S14^2-S14o^2; S23^2-S23o^2; S24^2-S24o^2; S34^2-S34o^2]; x = (inv(A)*b)*100;
%This gives three principal strains and three shearing strains % x = [ML AP SI ML-AP ML-SI AP-SI]