In vitro and in vivo biomechanical investigation of the clinical practice of disc prolapse prevention and rehabilitation

Underlying this thesis is the McKenzie school of thought, a physiotherapy approach that teaches clinicians to recommend particular exercises to their clients in an attempt to accelerate recovery/prevent recurrence of disc prolapse. The recommendations are based on an untested clinical theory that movements opposite to those that cause disc prolapse can achieve reversal of disc prolapse. Little consideration has been given scientifically to the reversal of the failure process of the lumbar discs. Three in vitro and one in vivo study were designed to attain a greater understanding of both disc failure and the mechanics of its clinical treatment responses and thereby provide a foundation for evidence-based practice.;Continuing from the disc height loss sub-classification of post-herniated in vitro discs, the second in vitro study in this thesis pursues alternate methods of creating herniation with the goal of creating herniation without causing more than thirty three percent disc height loss of the specimens. This study indicated that the in vitro model used in the first in vitro study displayed features from one end of the spectrum of damage seen clinically but was then the best-available. Combined these two studies provide a framework for interpretation of the results of the subsequent and third in vitro study in this thesis.;The focus of the third study is the mechanical investigation of the McKenzie clinical theory of the treatment response seen in vivo in prolapsed discs, which is that movements or positioning can alter the location of a displaced portion of nucleus in a prolapsed disc. The results indicate that the McKenzie approach works on some prolapsed discs and not on others. Consideration of the changes in disc height of the specimens during the testing procedures offers some understanding of the varied success of this approach and exposes a vast area of future research that will refine the clinical approach and mechanical understanding of this specific disc pathology.;The fourth study, an in vivo study, provides a first look at the kinematics and kinetics of the current in vivo application of this approach. The results of this study will enhance clinical practice by providing quantitative evidence of the relative peak motion of the McKenzie exercises as well as highlighting seemingly benign activities of daily living that involve levels of flexion, side bend and rotation sufficient to cause disc damage and even prolapse.;The first in vitro study in this thesis compared in vitro and in vivo herniated discs in an attempt to link the two and provide a more thorough understanding of the in vitro model proposed to test the mechanical theory underlying the McKenzie derangement approach. Ten C3/4 osteoligamentus porcine specimens were repeatedly flexed or flexed and side bent to result in posterior migration of the nucleus. Three of the 10 specimens had posterior migration of the nucleus. Statistically significant (p 33%) disc height loss occurred in all 10 specimens. The results provide a sub-classification of in vitro herniated discs that is similar to the spectrum of herniated discs that occurs in vivo.;The macroscopic goal of this thesis was to attain a greater understanding of the mechanics of both disc failure and its clinical treatment responses and thereby provide a foundation for evidence-based practice, a goal that was successfully achieved. This thesis ultimately challenged and increased our understanding of pathological discs while simultaneously adding information to assist clinical decision making. Several new contributions to the existing knowledge of lumbar spine biomechanics and clinical concepts of treating disc prolapse have been made. (Abstract shortened by UMI.).