• Shigeto Nakagawa, Ritsuro Ozaki, Yasuhiro Take, Ryo Iuchi, and Tatsuo Mae.
• Department of Orthopaedic Sports Medicine, Yukioka Hospital, Osaka, Japan nakagawa@yukioka.or.jp.
• Am J Sports Med. 2015 Nov 1; 43 (11): 2763-73.

BackgroundWhile the combination of a glenoid defect and a Hill-Sachs lesion in a shoulder with anterior instability has recently been termed a bipolar lesion, their relationship is unclear.PurposeTo investigate the relationship of the glenoid defect and Hill-Sachs lesion and the factors that influence the occurrence of these lesions as well as the recurrence of instability.Study DesignCase-control study; Level of evidence, 3.MethodsThe prevalence and size of both lesions were evaluated retrospectively by computed tomography scanning in 153 shoulders before arthroscopic Bankart repair. First, the relationship of lesion prevalence and size was investigated. Then, factors influencing the occurrence of bipolar lesions were assessed. Finally, the influence of these lesions on recurrence of instability was investigated in 103 shoulders followed for a minimum of 2 years.ResultsBipolar lesions, isolated glenoid defects/isolated Hill-Sachs lesions, and no lesion were detected in 86, 45, and 22 shoulders (56.2%, 29.4%, and 14.4%), respectively. As the glenoid defect became larger, the Hill-Sachs lesion also increased in size. However, the size of these lesions showed a weak correlation, and large Hill-Sachs lesions did not always coexist with large glenoid defects. The prevalence of bipolar lesions was 33.3% in shoulders with primary instability and 61.8% in shoulders with recurrent instability. In relation to the total events of dislocations/subluxations, the prevalence was 44.2% in shoulders with 1 to 5 events, 69.0% in shoulders with 6 to 10 events, and 82.8% in shoulders with ≥11 events. Regarding the type of sport, the prevalence was 58.9% in athletes playing collision sports, 53.3% in athletes playing contact sports, and 29.4% in athletes playing overhead sports. Postoperative recurrence of instability was 0% in shoulders without lesions, 0% with isolated Hill-Sachs lesions, 8.3% with isolated glenoid defects, and 29.4% with bipolar lesions. The presence of a bipolar lesion significantly influenced the recurrence rate, but lesion size did not.ConclusionThe 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.© 2015 The Author(s).

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