| Summary: | This thesis addresses changes in the supraspinatus muscle and tendon architecture, the relationship to fat infiltration and the effect of tear propagation using magnetic resonance imaging (MRI) and functional biomechanics testing using human tissues. The first hypothesis tests the relationship between the anterior and posterior portions of the supraspinatus and the central tendon when normal with no tear (NT), and pathological full thickness tears (FTT) groups. The changes in the pennation angles and central tendon associated with a FTT and the magnitude of the tear size were all statistically significant. The central tendon was found to lie anterior to the long axis of the supraspinous fossa as it passed laterally towards its insertion in the NT group. This relationship was reversed in the FTT group with the tendon lying more posteriorly or in the long axis. The second study hypothesis was that the degree of fatty infiltration of the supraspinatus is positively correlated to the maximal degree of central tendon retraction (CTR) from its insertion seen on the same MRI. The results found this relationship to be statistically significant. The aims of the cadaveric study were to establish the influence on abduction moments of full thickness tears with specific reference to tears to the central tendon. A new method of testing the biomechanics of in-vitro rotator cuff tears was developed through specimen-specific loading protocols through the use of a musculoskeletal dynamics model. A pair-wise comparison of the sections then revealed that the sectioning of the central tendon, regardless of whether the tear starts anteriorly or posteriorly, does the most significant damage to the moment producing capacity of supraspinatus. The overall contribution of this thesis is a clear understanding of the functional biomechanics of the central tendon of the supraspinatus in rotator cuff tears.
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