EFFECT OF A CHONDRAL-LABRAL DEFECT ON GLENOID CONCAVITY AND GLENOHUMERAL STABILITY - A CADAVERIC MODEL

One of the primary stabilizing mechanisms of the glenohumeral joint is concavity-compression, the maintenance of the humeral head in the con cave glenoid fossa by the compressive force generated by the surroundi ng muscles. This mechanism is active in all glenohumeral positions but it is particularly important in the functional mid-range, in which th e capsule and ligaments are slack. The effectiveness of concavity-comp ression in the stabilization of a joint can be characterized in terms of the ratio between the maximum dislocating force that can be stabili zed in a given direction and the load compressing the head into the gl enoid (the stability ratio). Glenoid concavity can be described by the lateral humeral displacement during translation across the glenoid. T he purpose of the present investigation was to characterize the concav ity and stability ratios of normal cadaveric glenoids, to measure the effect of an anteroinferior chondral-labral defect on these parameters , and to measure the effectiveness of a simulated operative reconstruc tion on the restoration of glenoid concavity and the stability ratio. The chondral-labral defect created in this study reduced the height of the glenoid by approximately 80 per cent and the stability ratio by a pproximately 65 per cent for translation in the direction of the defec t. Reconstruction of the anteroinferior aspect of the glenoid concavit y with use of an autogenous biceps-tendon graft restored normal values for these variables. CLINICAL RELEVANCE: Loss of glenoid concavity ma y be an important factor in glenohumeral instability, and reconstructi on of this concavity may effectively restore stability.