Multiple Subscapularis Tendon Sign: A New Risk Factor for Recurrence After Arthroscopic Anterior Shoulder Instability Surgery

BACKGROUND: Being able to predict recurrence after the treatment of shoulder instability would be helpful in planning the appropriate treatment. PURPOSE: To define the multiple subscapularis tendon sign (MSTS) as a novel anatomic variant and a possible risk factor for the recurrence of shoulder instability after anterior stabilization and to evaluate it, together with the other risk factors as described in the literature. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: A total of 87 patients met the study criteria and underwent arthroscopic stabilization for anterior shoulder instability. The MSTS was evaluated in this study group. Age, sex, hand dominance, number of preoperative shoulder dislocations, history of overhead or contact sports participation, type of labral lesion, number of anchors used in surgery, presence of the drive-through sign, presence of the MSTS, Oxford Shoulder Score results, and the association of these parameters with recurrence were assessed. The mean follow-up time was 81.0 ± 27.9 months (range, 48-139 months). RESULTS: Nine (10.3%) patients experienced recurrent instability. The presence of the MSTS (P = .009), existence of an anterior labroligamentous periosteal sleeve avulsion (ALPSA) lesion (P = .04), and history of overhead or contact sports participation (P = .04) were significant risk factors for recurrence. The recurrence rates were as follows: 30.7% with the MSTS; 40% with the MSTS and an ALPSA lesion; and 75% with the MSTS, an ALPSA lesion, and a history of overhead or contact sports participation. CONCLUSION: The MSTS is a variation of the anterior shoulder joint capsule. It is a sign of capsular insufficiency or thinning, which may be a risk factor for recurrence after anterior stabilization. Considering the low success rates of anterior capsulolabral repair in patients participating in overhead or contact sports, especially when an ALPSA lesion is present, encountering the MSTS during surgery in this at-risk group may be an indicator for the surgeon to choose the surgical procedure more carefully.