Injury mechanisms of the shoulder: Quantitative analysis of tendons and ligaments.

Abstract

The shoulder is one of the most frequently injured joints in the human musculoskeletal system, yet the etiology of shoulder injuries is not always well understood. This thesis is a compilation of studies that investigate specific mechanisms of injury associated with pathologic conditions of the shoulder. For each study, our approach was to quantify joint and tissue mechanics in a cadaveric shoulder model to lend insight into a particular mechanism of injury. Chapter 2 describes an investigation into the effect of inferior humeral subluxation on the creation of SLAP lesion injuries, and this study demonstrated that inferior subluxation of the humeral head significantly facilitates the generation of type II SLAP lesions. Chapter 3 is a fundamental investigation of the glenohumeral and coracohumeral ligaments' role on resisting external humeral rotation. This study demonstrated that the coracohumeral and inferior glenohumeral ligaments serve as the primary restraints to external rotation in the late-cocking position of the overhand throwing motion. Chapter 4 describes the validation of a novel, MRI-based technique for quantifying intratissue strains, a technique representing a significant advancement over conventional strain-measuring techniques. This approach demonstrated a displacement accuracy of 41 mum and a strain accuracy of within +/-0.6% for strains believed to be within the physiologic range. Chapter 5 describes application of the MRI-based strain measurement technique to quantifying intratendinous strains of the intact rotator cuff. This particular study suggests that the inferior region aspect of the supraspinatus tendon may be susceptible to damage during overhead activities. Chapter 6 extends the cadaveric model developed in Chapter 5 by investigating the effect of a simulated partial-thickness, articular-surface rotator cuff tears. This investigation demonstrated that a partial-thickness tear had a significant effect on rotator cuff tendon strain at nearly all glenohumeral joint positions. Chapter 7 summarizes the findings from Chapter 2--6 and suggests additional areas of study. Taken together, these chapters provide scientific and clinically relevant information which should improve our understanding of particular mechanisms of soft tissue injuries about the glenhumeral joint. In addition, these studies will stimulate new research hypotheses to further advance the scientific basis for clinical practice.