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 scoreeadjusted 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 degrees +/- 4.2 degrees vs -17.7 degrees +/- 5.5 degrees, 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.