Bone union was not always achieved after arthroscopic bony Bankart repair, and union was often delayed. Recurrence of instability was significantly more frequent when bone union failed. The size of the glenoid defect decreased significantly in shoulders with bone union.

The prevalence of bipolar lesions was approximately 60%. As glenoid defects became larger, Hill-Sachs lesions also enlarged, but there was no strong correlation. Bipolar lesions were frequent in patients with recurrent instability, patients with repetitive dislocation/subluxation, and those playing collision/contact sports. Instability showed a high recurrence rate in shoulders with bipolar lesions.

Background:Large glenoid rim defects in patients with traumatic anterior shoulder instability are often regarded as a contraindication for arthroscopic Bankart repair, with a defect of 20% to 27% considered as the critical size. While recurrence of dislocations, male sex, and collision sports were reported to be the significant factors influencing large glenoid defects, the influences of subluxations and more detailed types of sports were not investigated.Purpose:To investigate the influence of the number of dislocations and subluxations and type of sport on the occurrence and size of glenoid defects in detail.Study Design:Case-control study; Level of evidence, 3.Methods:A total of 223 shoulders (60 with primary instability, 163 with recurrent instability) were prospectively examined by computed tomography. Glenoid rim morphology was compared between primary and recurrent instability. In patients with recurrent instability, the relationship between the glenoid defect and the number of dislocations and subluxations was investigated. In addition, glenoid defects were compared among 49 male American football players, 41 male rugby players, 27 male baseball players, and 25 female athletes.Results:The mean extent of the glenoid defect was 3.5% in shoulders with primary instability and 11.3% in those with recurrent instability. A glenoid defect was detected in 108 shoulders (66.2%) with recurrent instability versus 12 shoulders (20%) with primary instability. Regarding the influence of the total number of dislocations/subluxations, the average extent of the glenoid defect was 6.3% in 85 shoulders with 2 to 5 events, 12.9% in 34 shoulders with 6 to 10 events, and 19.6% in 44 shoulders with 11 or more events. The glenoid defect became significantly larger along with an increasing number of recurrences. Although recurrent subluxation without dislocation also influenced the glenoid defect size, the number of dislocations did not. The average extent of the glenoid defect was 12.0% in rugby players, 8.9% in American football players, 4.7% in female athletes, and 4.5% in baseball players. Glenoid defects were significantly smaller in male baseball players and female athletes than in male collision athletes.Conclusion:The glenoid defect is significantly enlarged by damage due to recurrent dislocation and subluxation; therefore, glenoid rim morphology differs markedly between primary and recurrent instability. Glenoid defect size is also influenced by sex and by the type of sport.

Computed tomography is a useful imaging modality for evaluating Hill-Sachs lesions except for purely cartilaginous lesions. Hill-Sachs lesions were more frequent and larger when the primary episode was dislocation than when it was subluxation. Among patients with recurrent episodes of complete dislocation, the prevalence of Hill-Sachs lesions is increased, and the lesions are larger.

IV: retrospective or historical series.