A Finite Element Model of the Superior Glenoid Labrum

Abstract

Despite numerous studies on the function and pathologies of the shoulder joint’s superior glenoid labrum, controversy still exists concerning the mechanism of injury to the superior labral in the anterior to posterior direction (SLAP), and thus the optimal treatment. In this dissertation, the working hypothesis was that it is possible to use finite element models to explore the factors underlying the initiation and propagation of a SLAP lesion. First, the finite element model was validated for studying the tear mechanism in the superior labrum. An area of high strain correlated well with the location of SLAP tears observed clinically. The validated model was then used to evaluate the effect of both superior translation of the humeral head and tension on the long head of the biceps tendon on the strain in the intact labrum. The humeral head motion was found to have relatively greater effect than the biceps tension on the initiation of the SLAP tear. Repetitive micro-trauma or tissue fatigue rather than a single loading event is most likely to cause a mid-substance failure of the labrum. This work also tested the effect of the biceps tension on the propagation of SLAP tears using the finite element model. With loading of the biceps, the model predicted high strains at the edges of the tear suggesting a high risk for progression of the tear. For larger tears, the effect of the biceps was more pronounced. Based on this work, tear size is suggested as one criterion for determining the optimal treatment of the SLAP lesion. During development of the finite element model, simplifying assumptions were necessary. With careful consideration of the effect of these assumptions and simplifications on the results, the current work suggests a plausible mechanism of injury for SLAP lesions. This work is to identify the role of humeral head translation and biceps loading in the initiation and propagation of SLAP tears by examination of the predicted strain.