Variations In Glenoid Bony Morphology May Predict Recurrent Instability After Arthroscopic Bankart Repair
Authors: Vaswani Ravi S. , Sheean Andrew J. , Gasbarro Gregory , Como Christopher John , Kohut Kevin , Fourman Mitchell Stephen , Wilmot Andrew , Borrero Camilo , Vyas Dharmesh , Lin Albert 
Published: March 2020

Objectives: Variations in bony anatomy may be a significant risk factor for failure of stabilization surgery and could help explain the etiology of recurrent dislocations. Identifying these variations may help guide surgical decision making. The aim of this study was to develop a method to quantify bony morphology and measure glenoid and humeral head volume on MRI to identify risk factors for failure after Bankart repair. We hypothesized that the ratio of humeral head to glenoid volume and a shallower glenoid socket or greater radius of curvature would be significant risk factors in patients who failed stabilization surgery. Methods: This was a retrospective case-control study of 289 patients from 2005-2015. Inclusion criteria were primary anterior arthroscopic shoulder stabilization, no prior shoulder surgery, and traumatic etiology. Exclusion criteria were posterior labral pathology, multidirectional instability, connective tissue disorder, or concomitant rotator cuff pathology. Surgical failure was defined as a redislocation event and these cases were compared 1:2 to an age- and sex-matched control without recurrent instability. Demographic data was obtained by chart review. Pre-operative MR arthrograms were analyzed by two trained reviewers. Vitrea software (Vital Images, Minnetonka, MN) was utilized to measure the volume and radius of curvature of both the humeral head (Figure 1) and glenoid on T1 sequences. A larger radius of curvature corresponded to an overall shallower glenoid socket. Fisher exact and the student t test were used for statistical analysis with significant defined as p < 0.05. Results: Ninety-five patients met the inclusion criteria, 36 of whom were in the case group, with an average follow-up of 30.3 months. There was no difference between groups with regard to baseline demographic and radiographic parameters (Table 1). The average number of preoperative dislocations was significantly higher in the failure group (3.13 vs. 1.91, p < 0.05). The humeral head (67.8 ml vs 62.3 ml, p =0.13) and glenoid volume (13.7 ml vs 13.0 ml, p=0.42) were similar between the two groups, as was the ratio of the two (5.1 vs 4.9, p=0.30). The radius of curvature of the glenoid was slightly larger, or shallower, in the case group compared to the control group (23.8 mm vs 22.6 mm, p=0.02). The ratio of the radius of curvature of the humeral head to the glenoid was similar between the two groups (1.1 vs 1.1, p=0.11). Further analysis demonstrated that a greater portion of patients with a glenoid radius of curvature greater than 24.5 experienced a postoperative dislocation compared to those who had a smaller radius of curvature (63.6% vs 26.0%, p < 0.01) (Table 1). There was no significant difference between the number of preoperative dislocations between patients with larger or smaller glenoid radius of curvature (2.7 vs 2.3, p = 0.57). Conclusion: Using a novel method of quantifying the bony morphology, our results demonstrate that a larger radius of curvature, particularly greater than 24.5 mm, which is indicative of a shallower glenoid, may predispose patients to failure following a primary arthroscopic Bankart. These findings suggest that the overall bony concavity of the glenoid may play an inherent role regarding stability. [Table: see text]