Association of Traumatic and Atraumatic Posterior Shoulder Instability With Glenoid Retroversion and Outcomes After Arthroscopic Capsulolabral Repair.

PURPOSE To compare glenoid retroversion and functional outcomes between patients with traumatic onset of posterior shoulder instability (PSI) and patients with atraumatic onset of PSI. METHODS Patients with PSI who underwent arthroscopic posterior capsulolabral anchor repair, were active in sports, and had undergone surgery a minimum of 2 years earlier were included. Traumatic onset was defined as PSI that occurred after a trauma with the shoulder in adduction, flexion, and internal rotation in patients with no history of instability. Subjective evaluations were obtained with the American Shoulder and Elbow Surgeons (ASES); Quick Disabilities of the Arm, Shoulder and Hand; Single Assessment Numeric Evaluation (SANE); and Short Form 12 Physical Component Summary scores preoperatively and after a minimum 2-year follow-up postoperatively. Additional questions assessed return to sport and shoulder stability. Glenoid version was measured with a 2-dimensional glenoid vault method on magnetic resonance imaging. RESULTS A total of 41 shoulders in 38 patients were eligible for inclusion (3 female and 35 male patients; mean age, 27.6 years; age range, 13 to 66 years). Three patients refused participation, and 2 patients required subsequent surgery for failure. Postoperative outcomes were available for 32 of the remaining 36 shoulders (89%) with a mean follow-up of 4.1 years (range, 2.0 to 7.8 years; 20 atraumatic and 12 traumatic). The ASES score improved significantly in both groups (P < .03), whereas the SANE; Quick Disabilities of the Arm, Shoulder and Hand; and Short Form 12 Physical Component Summary scores only significantly improved for patients with traumatic PSI (P < .02). Baseline score-adjusted comparison between groups showed that the postoperative median ASES scores (atraumatic, 95.8; traumatic, 99.9) and SANE scores (atraumatic, 86.5; traumatic, 98.0) were significantly more improved in patients with traumatic PSI (P = .01 and P = .012, respectively). Atraumatic PSI was associated with significantly higher glenoid retroversion (-21.8° ± 4.2° vs -17.7° ± 5.5°, P = .032). There was no significant difference regarding return to sport (P = .375) or postoperative re-dislocations (P = .99) between the groups. CONCLUSIONS Atraumatic onset of PSI was associated with higher degrees of glenoid retroversion and less favorable functional outcomes of arthroscopic posterior capsulolabral anchor repair than traumatic PSI. LEVEL OF EVIDENCE Level III, retrospective case-control study.