Changes of Bipolar Bone Defect Size After Arthroscopic Bankart Repair for Traumatic Anterior Shoulder Instability: Evaluation Using a Scoring System and Influence on Postoperative Recurrence

BACKGROUND: The combination of a glenoid defect and a Hill-Sachs lesion in shoulders with traumatic anterior instability has been termed bipolar bone loss, and the preoperative size of these lesions has been reported to influence postoperative recurrence of instability after arthroscopic Bankart repair. PURPOSE: To investigate the influence of postoperative bipolar bone defect size on postoperative recurrence of instability. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: A total of 64 male collision/contact athletes (69 shoulders) were evaluated for a minimum of 2 years after surgery, and the pre- and postoperative sizes of both lesions (glenoid defect and Hill-Sachs) were evaluated retrospectively with 3-dimensional computed tomography. The sports played by the athletes included rugby (n = 28 shoulders), American football (n = 24 shoulders), and other collision/contact sports (n = 17 shoulders). Glenoid defects and Hill-Sachs lesions were classified into 5 size categories and assigned scores from 0 (no defect) to 4 (very large defect). Patients were then classified according to the total score (sum of the scores for both lesions). The influence of pre- and postoperative bipolar bone defect sizes on recurrence of instability was investigated by using the total scores for bipolar bone defects. The influence of postoperative glenoid morphology (normal preoperative glenoid, preoperative glenoid erosion, bone union after arthroscopic bony Bankart repair [ABBR], or nonunion after ABBR) was also investigated, as well as changes in shoulders with a preoperative off-track Hill-Sachs lesion. RESULTS: Of 69 shoulders, 15 (21.7%) developed recurrent instability after surgery. The postoperative recurrence rate was 0% in shoulders with a total score ≤1, while the recurrence rate was consistently higher in shoulders with a total score ≥2 at both pre- and postoperative evaluation (mean, 28.8% and 32.6%, respectively). Postoperative recurrence was uncommon when there was a normal preoperative glenoid or bone union after ABBR, while it was frequent in shoulders with preoperative glenoid erosion or shoulders with nonunion after ABBR and a total score ≥2. An off-track lesion was recognized in 9 shoulders preoperatively. It was transformed to on-track lesions in 4 of the 5 shoulders showing bone union after ABBR, and there was no recurrence in the 5 shoulders with bone union. In contrast, postoperative recurrence of instability occurred in 3 of the 4 shoulders without bone union. CONCLUSION: Postoperative recurrence was influenced by the pre- and postoperative size of bipolar bone defects. Recurrence was uncommon if bone union was achieved after ABBR, even if there had been an off-track lesion preoperatively.