Effect of Humeral Head Defect Size on Glenohumeral Stability

Abstract

Background Hill-Sachs lesions are often present with recurrent shoulder instability and may be a cause of failed Bankart repair. Hypothesis Glenohumeral joint stability decreases with increasingly larger humeral head defects. Study Design Descriptive laboratory study. Methods Humeral head defects, 1/8, 3/8, 5/8, and 7/8 of the humeral head radius, were created in 8 human cadaveric shoulders, simulating Hill-Sachs defects. Testing positions included 45° and 90° of abduction and 40° of internal rotation, neutral, and 40° of external rotation. Testing occurred at each defect size sequentially from smallest to largest for all abduction and rotation combinations. The humeral head was translated at 0.5 mm/s 45° anteroinferiorly to the horizontal glenoid axis until dislocation. Distance to dislocation, defined as humeral head translation until it began to subluxate, was the primary outcome measure. Results Significant factors by ANOVA were rotation (P < .001) and defect size (P < .001). There was no difference for the 2 abduction angles. External rotation of 40° significantly reduced distance to dislocation compared with neutral and 40° internal rotation (P < .001). Osteotomies of 5/8 and 7/8 radius significantly decreased distance to dislocation over the intact state (P = .009 and P < .001, respectively). Post hoc analysis determined significant differences for the rotational positions. Decreased distance to dislocation occurred at 5/8 radius osteotomy at 40° external rotation with 90° of abduction (P = .008). For the 7/8 radius osteotomy at 90° abduction, there was a decreased distance to dislocation for neutral and 40° external rotation (P < .001); at 45° abduction, there was a decreased distance to dislocation at 40° external rotation (P < .001). With the humerus internally rotated, there was no significant change in distance to dislocation. Conclusion Glenohumeral stability decreases at a 5/8 radius defect in external rotation and abduction. At 7/8 radius, there was a further decrease in stability at neutral and external rotation. Clinical Relevance Defects of 5/8 the humeral head radius may require treatment to decrease the failure rate of shoulder instability repair.