CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Number 391, pp. 266–274 © 2001 Lippincott Williams & Wilkins, Inc. Strain in the Human Medial Collateral Ligament During Valgus Loading of the Knee John C. Gardiner, PhD*; Jeffrey A. Weiss, PhD*; and Thomas D. Rosenberg, MD*,** The medial collateral ligament is one of the most ligament and that this distribution of strain frequently injured ligaments in the knee. Al- changes with flexion angle and with the applica- though the medial collateral ligament is known tion of a valgus torque. Strain in the posterior to provide a primary restraint to valgus and ex- and central portions of the medial collateral lig- ternal rotations, details regarding its precise ament generally decreased with increasing flex- mechanical function are unknown. In this study, ion angle, whereas strain in the anterior fibers strain in the medial collateral ligament of eight remained relatively constant with changes in knees from male cadavers was measured during flexion angle. The highest strains in the medial valgus loading. A material testing machine was collateral ligament were found at full extension used to apply 10 cycles of varus and valgus ro- on the posterior side of the medial collateral lig- tation to limits of ؎10.0 N-m at flexion angles of ament near the femoral insertion. These data -0؇, 30؇, 60؇, and 90؇. A three-dimensional motion support clinical findings that suggest the femo analysis system measured local tissue strain on ral insertion is the most common location for the medial collateral ligament surface within 12 medial collateral ligament injuries. regions encompassing nearly the entire medial collateral ligament surface. Results indicated that strain is significantly different in different The medial collateral ligament is one of the regions over the surface of the medial collateral most frequently injured ligaments in the knee.12 Medial collateral ligament injuries of- ten occur during sports such as football or soc- From the *Department of Bioengineering, The Univer- cer from a direct blow to the lateral side of the sity of Utah; and **The Orthopedic Specialty Hospital, Salt Lake City, UT. knee or because of external rotation of the tibia Supported by Whitaker Foundation Biomedical Research during alpine skiing. Clinical reports suggest and Transition Grants and National Institutes of Health injuries to the medial collateral ligament most Grant Number AR47369. commonly are located near the femoral inser- Reprint requests to Jeffrey A. Weiss, PhD, The Univer- tion.10,11 After an isolated medial collateral sity of Utah, Department of Bioengineering, 50 South Central Campus Drive, Room 2480, Salt Lake City, UT ligament injury, adequate healing often occurs 84112. without surgical intervention. However, many Received: September 22, 2000. medial collateral ligament injuries are accom- Revised: December 8, 2000; February 12, 2001. panied by disruption of the anterior cruciate Accepted: March 13, 2001. ligament, resulting in a poor healing outcome 266 Number 391 October, 2001 Medial Collateral Ligament Strain 267 for the medial collateral ligament and the an- can be a difficult and time-consuming process. terior cruciate ligament, leading to chronic in- Accurate experimental input parameters such stability of the knee. A complete understand- as in situ strain are essential for creating sub- ing of the normal stress and strain state in the ject-specific models. The validation of com- medial collateral ligament can aid in the un- putational models also is dependent on exper- derstanding and prevention of ligament in- imental data to confirm that model-predicted juries and in the formulation of treatments. quantities such as local tissue strain or joint Previous studies of the mechanical function stiffness are accurate. Once validated, these of the medial collateral ligament can be cate- models can provide a valuable tool for under- gorized broadly as studies of ligament cutting standing the mechanical function of normal that measured changes in joint laxity after cut- and diseased joints and ligaments and for as- ting specific regions of the medial collateral sessing the effects of clinical interventions. ligament and other structures,5 or studies that Despite the importance of the medial col- measured overall load in the ligament14,15 or lateral ligament in maintaining joint stability, local tissue strain1,3,8 during external loading. many fundamental questions remain regard- Studies of ligament cutting and measurements ing its precise mechanical function. Measure- of tissue load have shown that the medial col- ments of medial collateral ligament strain re- lateral ligament provides a primary restraint to ported in previous studies have been limited to valgus rotation and a secondary restraint to ex- few locations within the tissue, despite indica- ternal rotation and anterior and posterior trans- tions that strain is highly inhomogeneous over lations. Measurements of local tissue strain the entire medial collateral ligament sur- provide detailed information regarding the rel- face.1,3,8 In particular, strain in the region of ative importance of different regions of the the medial collateral ligament often referred to medial collateral ligament during specific as the posterior oblique ligament has not been loading conditions. Measurements have indi- quantified previously, despite indications of cated that the strain distribution is inhomoge- its importance from ligament cutting studies.5 neous over the medial collateral ligament sur- In addition, strain measurements often have face and that this nonuniform distribution been made relative to a loaded reference changes with flexion angle and with the appli- state.1 This procedure may grossly underesti- cation of external loads. mate actual tissue strain levels by assuming a Computational modeling techniques such zero strain value exists in tissue that actually as the finite element method provide an addi- may be loaded at a level of 3% or more. Quan- tional means to assess medial collateral liga- tifying the initial tension in ligaments is an es- ment function and situations that may lead to sential step in the construction of accurate injury.2,4 Computational models of joints have computational models. The objective of the the potential to predict quantities such as tis- current study was to quantify the strain distri- sue stress and joint contact pressure that can be bution in the entire medial collateral ligament difficult or impossible to measure in experi- during passive flexion and valgus loading. It mental or clinical settings. Computational was hypothesized that the strain distribution in models also provide a repeatable tool for eval- the medial collateral ligament is nonuniform uating multiple clinical treatments, an ap- and that this distribution changes with flexion proach that can eliminate the large intersubject angle and with the application of a valgus variability that often limits the sensitivity of torque. It also was hypothesized that strain experimental and clinical investigations. Mus- would be highest near the femoral insertion in culoskeletal modeling methodologies and com- correspondence with clinically observed in- puting power have advanced significantly in jury patterns and that strain in the anterior por- recent years. Unfortunately, the effective con- tion of the medial collateral ligament would struction and validation of complex models decrease with increases in knee flexion angle. Clinical Orthopaedics 268 Gardiner et al and Related Research MATERIALS AND METHODS loading served to precondition the soft tissue struc- tures of the knee. The varus and valgus rotation was Sample Population and Preparation applied at 1.0Њ/second to torque limits of Ϯ 10.0 N- m. The rotation speed was chosen to provide qua- Eight knees from male cadavers (age, 50 Ϯ 7 years) sistatic loading, where tissue viscoelastic effects were used in the current study. The fresh-frozen and inertial effects of the kinematic fixtures could specimens were thawed at room temperature be minimized. The torque limit of 10 N-m is suffi- overnight before dissection and were inspected for ciently large to enter the terminal stiffness region of signs of previous injury or arthritis. All periarticu- the varus and valgus torque rotation curve but is lar soft tissue was removed until only the medial much smaller than the torque required to induce tis- collateral, lateral collateral, anterior cruciate, and sue damage, allowing multiple tests to be done with posterior cruciate ligaments and medial and lateral the same specimen. All data analysis was per- menisci remained intact (Fig 1). The femur, tibia, formed using the results obtained during the load- and fibula were potted in mounting tubes using a ing phase of the tenth valgus cycle. low-melt alloy. During all dissection and testing, the tissue was kept continuously moist with 0.9% Strain Measurement buffered saline. All testing was completed within 5 hours, during which time no noticeable changes in A noncontact three-dimensional motion analysis sys- the tissue were observed. tem (Peak Performance Technologies, Englewood, CO) was used for simultaneous measurement of Kinematic Testing strain at multiple locations on the medial collateral ligament surface. A custom calibration frame was The knees were mounted in custom fixtures on a bi- constructed, and 18 retroreflective fiducial markers axial material testing machine (MTS, Eden Prairie, were attached to the frame. The coordinates of the MN) that allowed application of varus and