Investigation of intrinsic spine muscle properties to improve musculoskeletal spine modelling by Derek Peter Zwambag A Thesis Presented to The University of Guelph In partial fulfillment of requirements for the degree of Doctor of Philosophy In Human Health and Nutritional Sciences Guelph, Ontario, Canada ©Derek Zwambag, October 2016 ABSTRACT Investigation of intrinsic spine muscle properties to improve musculoskeletal spine modelling Derek Peter Zwambag Advisor: University of Guelph, 2016 Dr. Stephen H.M. Brown Spine muscles are known to generate large compressive loads and play a vital role in spine stabilization. Spine loads and stability are often estimated using computational models; yet, models cannot account for inherent differences in intrinsic muscle properties, as these data are unavailable. This dissertation was borne out of this need to further understand the characteristics of spine muscles. Part A of this dissertation consisted of three experiments each designed to address a specific research question. Each experiment also generated normative data, which were combined in Part B to create a custom musculoskeletal spine model capable of predicting dynamic active and passive muscle moments. Generic muscle models do not accurately predict whole muscle passive stresses. Experiment I investigated passive muscle stress differences following facet joint injury. Passive muscle stresses were not altered 28 days following injury. Data from control animals were used to model passive muscle stresses throughout physiological sarcomere lengths. Experiment II was designed to determine the sarcomere lengths of spine muscles based on posture. Physiological sarcomere lengths were measured from human cadavers in a neutral posture using laser diffraction; sarcomeres of muscles posterior to the spine were shorter than muscles anterior to the spine. During modelled flexion, posterior muscles became strained and sarcomeres approached ii the optimal length for active force production. These data were incorporated into the model to estimate sarcomere lengths of spine muscles based on spine posture. Spine muscles display a unique phenomenon known as ‘flexion relaxation’, which occurs when extensor muscles ‘turn off’ despite substantial demand near full trunk flexion. Passive tissues are believed to support the weight of the upper body. Experiment III further tested this proposed mechanism using a pulley system to manipulate the weight of the upper body. These data were used to validate the active and passive muscle moments predicted by the musculoskeletal model. The model predicted: a) the occurrence of flexion relaxation; b) that decreasing the external moment caused flexion relaxation to occur earlier; and c) the requirement for abdominal muscle activity at full flexion. The model also suggested that muscle generates greater passive moments than ligaments in full flexion. iii Acknowledgements Thank you to my examining committee members Drs. Jack Callaghan, Geoff Power, John Srbely, and Stephen Brown. I appreciate the time you put into reading this thesis and all your comments and suggestions. Your efforts and passion for biomechanics have improved the quality of this thesis. I would also like to thank my comprehensive examination committee members Drs. Howard Vernon, Cheryle Séguin, Karen Gordon, and Stephen Brown. I was fortunate to be able to study the spine from the points of view of a clinician, biologist, engineer, and biomechanist. I am a better researcher thanks to all of you! I can’t thank my advisor Dr. Stephen Brown enough. Thank you very much for allowing me to study a broad range of interests. I am grateful for all your guidance, motivation, and scientific insight. You are an amazing role model, which I will strive to emulate moving forward. Thanks to Shawn Beaudette, my fellow Brown lab PhD student. You’ve been a great friend, teammate, housemate, labmate, and co-author. I’m excited to see all that you will accomplish in the future. A big thank you to Kelsey Gsell, Dennis Larson, Lydia Frost, Alex Harriss, Grace Glofcheskie, and the extended biomechanics group and faculty for making HHNS a great place to work and learn. Finally, thank you very much to my parents Gerald and Anja Zwambag, my fiancée Jacqueline Nixon, and my siblings for supporting me and encouraging me throughout this very long process. Thanks for allowing me to pursue my dream and stay in school for this long. iv Table of Contents ABSTRACT…………………………………………………………………………… ii Acknowledgements…………………………………………………………….. iv Table of contents………………………………………………………………... v List of tables……………………………………………………………………….. viii List of figures……………………………………………………………………… ix Chapter 1: Introduction………………………………………………………. 1 1.1 Passive muscle modelling…………………………………………………… 1 1.2 Muscle anatomy………………………………………………………………….. 5 1.2.1 Multifidus………………………………………………………………….. 6 1.2.2 Erector spinae……………………………………………………………. 7 1.2.3 Latissimus dorsi…………………………………………………………. 8 1.2.4 Quadratus lumborum…………………………………………………. 8 1.2.5 Psoas major…………………..…………………………………………… 8 1.2.6 Abdominal muscles…………….……………………………………… 9 1.3 Dissertation overview……………….………………………………………… 10 1.3.1 Part A: Experiment 1………….……………………………………… 10 1.3.2 Part A: Experiment 2………….……………………………………… 11 1.3.3 Part A: Experiment 3………….……………………………………… 11 1.3.4 Part B: Musculoskeletal Model…………………………………… 11 1.4 Statement of ethics……………….…………………………………………..… 12 Chapter 2: Part A- Experiment I………………………………………….. 13 Disruption of erector spinae aponeurosis and facet compression in a rat model does not alter the passive mechanics of spine muscles after four weeks of recovery 2.1 Chapter overview……………….………………………………….....………… 13 2.2 Introduction……………….………………………………………………….…… 13 2.3 Methods……………….……………………………………………………………… 16 2.3.1 Surgical groups………………………………………………………….. 16 2.3.2 Tissue samples………………………………………………………..…. 18 2.3.3 Mechanical testing……………………..………………………………. 19 2.3.4 Data analysis……………………………..………………………………. 20 2.3.5 Behavioural testing……………………...……………………………. 21 2.3.6 Statistical analysis……………………………..………………………. 22 2.4 Results……………….……………………………………………………………..… 22 2.4.1 Elastic moduli……………………………………………………………. 22 2.4.2 Slack length………………………………………………………………. 24 2.4.3 Passive stress-length relationship………………………...……. 26 2.4.4 Behavioural testing……………………………………………………. 27 2.4.5 Histology……………………………………..……………………………. 27 2.5 Discussion……………….…………………………………………….…………… 28 v 2.5.1 Effect of Incision surgery…………………………………………… 29 2.5.2 Effect of Compression surgery ……………………….………… 30 2.5.3 Future directions………………………………………….….………. 32 2.6 Bridge summary……………….………………………….…………………… 34 Chapter 3: Part A- Experiment II…………………..…………………... 39 Sarcomere length organization as a design for cooperative function amongst all lumbar spine muscles 3.1 Chapter overview……………….………………….………………………… 39 3.2 Introduction……………….…………………………………….……………… 40 3.3 Materials and methods……………….……………….…………………… 43 3.3.1 Cadaveric donors …………………………….…..…………………. 43 3.3.2 Sarcomere length measurement………………………………. 44 3.3.3 Modelled operating ranges………………………………………. 45 3.3.4 Statistical analysis…………………………………………………... 48 3.4 Results……………….…………………………………………………………….. 48 3.4.1 Neutral spine cadaveric sarcomere lengths……………… 48 3.4.2 Modelled sarcomere lengths……………………………………. 50 3.4.2.1 Flexion and extension…………..…………………………. 50 3.4.2.2 Lateral bending………………………………………………. 54 3.4.2.3 Axial rotation…………………………………………………. 55 3.5 Discussion……………….……………………………………………………..… 55 3.6 Bridge summary……………….……………………………………………… 61 Chapter 4: Part A- Experiment III……………………………,,………. 63 Decreasing the required lumbar extensor moment induces earlier onset of flexion relaxation 4.1 Chapter overview……………….……………………………………….…… 63 4.2 Introduction……………….………………………………………………….… 64 4.3 Methods……………….…………………………………………………………… 67 4.3.1 Participant characteristics…………..…………………………... 67 4.3.2 Experimental set-up…………..…………………………………….. 67 4.3.3 Protocol…………..………………………………………………………. 70 4.3.4 Data processing…………..……………………………………………. 71 4.3.5 Statistical analysis…………..……………………………..…………. 72 4.4 Results……………….……………………………………………………………… 73 4.4.1 Lumbar erector spinae…………….………..………………………. 73 4.4.2 Abdominal muscles…………………..…………..……….…………. 75 4.4.3 Additional muscles…………..………………………………………. 78 4.5 Discussion……………….……………………………….……………………..… 80 4.6 Bridge summary……………….…………………………….………………… 86 Chapter 5: Part B- Musculoskeletal model………………………… 88 5.1 Chapter overview……………….…………………………………………..… 88 vi 5.2 Passive muscle model……………….……………………………………… 90 5.2.1 Model development…………..…………………………….………. 90 5.2.2 Additional passive muscle models…………..……..…………. 93 5.2.3 Results…………..…………………………………………………..……. 95 5.2.3.1 Passive muscle stress-length relationship………… 95 5.2.3.2 L4-L5 sagittal passive muscle moment……………... 96 5.2.4 Implications of these findings…………..…………………….…. 99 5.3 Model of flexion relaxation……………….…………………………..…… 103 5.3.1 Model development…………..……………………………………... 103 5.3.2 Results of the model…………..……………………..………………. 108 5.3.2.1 Moments throughout trunk flexion movements…. 108 5.3.2.2 Moments at the critical point of flexion relaxation 110 5.3.3. Implications of these findings…………..………………………. 111 Chapter 6: Conclusions and future directions……………..…..… 114 Chapter 7: References…………………………………………………..…… 116 vii List of tables Table 2.1: Effects of surgical group, muscle, and sample type on the passive elastic moduli of rat spine muscles. 23 Table 2.2: Effects of surgical group, muscle, and muscle size on the slack sarcomere length of rat spine muscles. 25 Table 2.3: Spline