Functional Partitioning of the Human Lumbar Multifidus: An Analysis of Muscle Architecture, Nerve and Fiber Type Distribution using a Novel 3D in Situ Approach by Alessandro Rosatelli A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Institute of Medical Science University of Toronto © Copyright by Alessandro Rosatelli 2010 Functional Partitioning of the Human Lumbar Multifidus: An Analysis of Muscle Architecture, Nerve and Fiber Type Distribution using a Novel 3D in situ Approach Alessandro L Rosatelli Doctor of Philosophy Institute of Medical Science University of Toronto 2010 Abstract Muscle architecture, innervation pattern and fiber type distribution of lumbar multifidus (LMT) throughout its volume was quantified. Musculotendinous (n=10) and neural components (n=3) were dissected and digitized from thirteen embalmed cadaveric specimens. The data were imported into Autodesk® Maya® 2008 to generate 3D neuromuscular models of each specimen. Architectural parameters (fiber bundle length, FBL; fiber bundle angle, FBA; tendon length) were quantified from the models using customized software. The medial branch of the posterior rami (L1-L5) was traced through LMT to determine its distribution. Using immunohistochemistry, Type I/II muscle fibers were identified in 29 muscle biopsies from one fresh frozen specimen. The total area and number of each cell type was calculated using Visiopharm® (image analysis software). Architectural and fiber type data were analyzed using ANOVA with Tukey’s post-hoc test (p ≤ 0.05). ii From L1-L4, LMT had three architecturally distinct regions: superficial, intermediate and deep. At L5, intermediate LMT was absent. Mean FBL decreased significantly from superficial (5.8 ± 1.6cm) to deep regions (2.9 ± 1.1cm) as did volume (superficial, 5.6 ± 2.3ml; deep, 0.7 ± 0.3ml). In contrast, mean FBA increased from superficial to deep. The medial branch of the posterior ramus (L1-L5) supplied the five bands of LMT. Each medial branch in turn divided to supply the deep, intermediate and superficial regions separately. The area occupied by Type I fibers was significantly less (p< 0.01) in the deep (56%) compared with the superficial regions (75%). Based on architecture and morphology, superficial LMT with the longest FBL and relatively small FBA is well designed for torque production and controlling the lumbar lordosis. Intermediate LMT with significantly longer FBL compared with the deep region and with its caudal to cranial line of action may help to control intersegmental stability. Furthermore, the absence of intermediate LMT at L5 and may contribute to the higher incidence of instability observed at the lumbosacral junction. Deep LMT with its short FBL, large FBA and proximity to the axis of spinal rotation may function to provide proprioceptive input to the CNS rather than a primary stabilizer of the lumbar spine. iii Acknowledgments If I have achieved anything thus far it is because I had the opportunity to work with some truly great people. First and foremost I would like to thank my mentor and research supervisor Dr. Anne Agur who has provided me support, advice and encouragement throughout my graduate career. She has challenged me, pushed me and made me strive far beyond what I perceived to be possible. My sincerest thanks go to my advisory committee consisting of Dr. Bernie Liebgott, Dr. Karan Singh, and Dr. Sharon Switzer-McIntyre for their expert advice, assistance and guidance. I would like to recognize the participation of both my internal and external examiners, Dr. Scott Thomas and Dr. Thomas Quinn. I also extend my gratitude to Dr. Mike Wiley and Dr. Ian Taylor for reviewing this thesis and providing much appreciated feedback. I thank my fellow graduate students in the Division of Anatomy, Department of Surgery: Soo Kim, Christopher Yuen, as well as Kajeandra and Mayo Ravichandiran who were instrumental in software development and implementation. Thanks go to the anatomy technical staff of Bill Wood, Terry Irvine, and Jerry Topham for their expertise in preparing the cadaveric specimens used in my graduate studies. Marianne Rogers at Mt. Sinai Hospital, spent many hours teaching me how to use the image analysis software used to examine muscle biopsy specimens, I extend my deepest gratitude. Your assistance was greatly valued. Most importantly, I would like to thank my family for their unwavering love and support. Their constant encouragement lifted my spirits and lightened the journey, particularly when it was needed most. A special dedication goes to my parents from iv whom I drew strength by emulating their perseverance, desire, and dedication. Lastly, to my wife Andrea, my best friend and most critical reviewer, thank you for believing in me. Acknowledgement is made to the AO/ASIF Foundation, Switzerland and the Department of Surgery, University of Toronto for financial support. v Table of Contents Page Abstract ............................................................................................................................. ii Acknowledgments............................................................................................................ iv Table of Contents............................................................................................................. vi List of Figures .................................................................................................................. xi List of Tables..................................................................................................................xiv List of Abbreviations .......................................................................................................xv Chapter 1: Introduction....................................................................................................1 1.1 Contents of Thesis................................................................................................ 5 Chapter 2: Literature Survey ...........................................................................................6 2.1 Muscle Architecture............................................................................................. 6 2.1.1 Overview of Architectural Parameters.................................................. 6 2.1.1.1 Fiber Bundle Length (FBL) ....................................................... 9 2.1.1.2 Fiber Bundle Angle (FBA) ...................................................... 11 2.1.1.3 Muscle Volume and Mass........................................................ 11 2.1.1.4 Physiological Cross Sectional Area (PCSA) ........................... 12 2.1.1.5 Fiber Type Distribution ........................................................... 13 2.1.2 Functional Significance of Muscle Architecture ................................ 14 2.2 Why Study Human Lumbar Multifidus Architecture? ...................................... 17 2.3 Previous Studies on the Morphology, Architecture, Innervation and Fiber Type distribution of LMT .................................................................................. 19 2.3.1 Morphology of LMT........................................................................... 19 2.3.2 Architecture of LMT........................................................................... 20 vi 2.3.2.1 Qualitative/Descriptive Studies ............................................... 20 2.3.2.2 Quantitative Cadaveric Studies and their Results.................... 24 2.3.2.2.1 Quantification of FBL....................................................... 24 2.3.2.2.2 Quantification of FBA ...................................................... 25 2.3.2.2.3 Quantification of Volume ................................................. 29 2.3.3 Innervation of LMT ............................................................................ 29 2.3.3.1 Motor Control of Lumbar Stability.......................................... 30 2.3.4 Fiber Typing of LMT.......................................................................... 31 2.3.4.1 Cadaveric Investigations.......................................................... 32 2.3.4.2 In Vivo Investigation ............................................................... 33 2.3.4.3 Comparison of Cadaveric and In Vivo Measurements............ 34 2.4 Functions of LMT based of Morphological, Biomechanical, Electromyographic and Clinical Evidence......................................................... 35 2.4.1 Morphological Evidence..................................................................... 35 2.4.2 Biomechanical Evidence..................................................................... 37 2.4.2.1 Role of LMT in Torque Production......................................... 37 2.4.2.2 Role of LMT in Spinal Stability .............................................. 39 2.4.2.2.1 Role of LMT in Maintaining the Lumbar Lordosis.......... 39 2.4.2.2.2 Role of LMT in Controlling Shear Forces........................ 40 2.4.2.2.3 Biomechanical Models for the Stability Role................... 40 2.4.2.2.4 Role in Providing Stiffness to the Spine........................... 44 2.4.3 Electromyographic Evidence.............................................................. 45 2.4.3.1 LMT Activity Involved in the Maintenance of Posture........... 46 vii 2.4.3.2 LMT Activity in Active Lumbar Movements ......................... 46 2.4.3.3 LMT Activity During Internal and External Perturbations of the Trunk.........................................................................