Hill-Sachs defects and repair using osteoarticular allograft transplantation: biomechanical analysis using a joint compression model.

Background: Humeral head defects have been associated with failed anterior shoulder instability repairs. Quantitative data are required to determine (1) the critical defect size for consideration of surgical repair and (2) the ability of proposed repair techniques to restore normal joint function.

Hypotheses: Increasing defect size will decrease stability and anterior translation before dislocation.

The current anatomical description of the inferior glenohumeral ligament does not correlate with its functional role in positions of external rotation.

The objective of this study was to determine the strain distribution in the inferior glenohumeral ligament at 0 degree, 30 degrees, and 60 degrees of external rotation with an anterior load applied to the joint. Five cadaver shoulders were dissected free of all soft tissue except the glenohumeral capsule and a 7 x 11 grid of strain markers were affixed to the inferior glenohumeral ligament. The location of these strain markers was then determined for a reference strain configuration and while a 25 N anterior load was applied to simulate a clinical exam for instability.