Posterior Shoulder Instability: Does Glenoid Retroversion Predict Recurrence and Contralateral Instability?

Purpose: To determine whether glenoid retroversion is a predictor of posterior shoulder instability, contralateral instability, or recurrent instability in patients with traumatic, contact-related posterior shoulder instability. Methods: Patients who underwent shoulder stabilization by 2 senior orthopaedic sport surgeons were identified retrospectively. Patients with a connective tissue disorder, multidirectional instability, or non-trauma-induced pathology were excluded. Patients with a glenoid lesion involving greater than 25% of the glenoid or an engaging humeral lesion were also excluded. Thus patients with a traumatic injury and a magnetic resonance imaging scan available for review were included. Magnetic resonance imaging scans were reviewed, and glenoid version was measured using the glenoid vault method. Charts were reviewed for epidemiologic data, recurrent instability requiring reoperation, evidence of glenoid/humeral bone lesions, and contralateral shoulder instability requiring surgery. Both recurrence and contralateral injury were defined based on having repeat surgery. Results: We identified 143 patients who met the inclusion criteria. Twenty-eight patients had posterior instability, whereas 115 patients had anterior instability. Patients with posterior instability had significantly more glenoid retroversion than patients with anterior instability (-15.4 degrees +/- 5.14 degrees v -12.1 degrees +/- 6.9 degrees; P < .016). Patients with retroversion of more than -16 degrees showed a higher incidence of contralateral injuries (P < .036). However, no difference in postsurgical recurrent instability was noted. Conclusions: Our data show that patients with posterior instability have a higher incidence of having a retroverted glenoid. Patients with increased retroversion showed increased posterior contralateral instability. Furthermore, patients with posterior instability and no humeral bone lesions may be more likely to incur contralateral injuries than those with humeral lesions. These data suggest that glenoid version and concomitant injury patterns may be used to help physicians counsel patients on their future risks of contralateral injury.