Anterior and posterior glenoid bone loss in patients receiving surgery for glenohumeral instability is not the same: a comparative 3-dimensional imaging analysis

BACKGROUND: Anterior and posterior glenoid bone loss morphology have both been individually and morphologically described in previous studies. While there exists substantial literature on anterior bone loss, and emerging evidence describing posterior bone loss, a direct comparison between the two is lacking in the current literature. The purpose of this study is to quantitatively compare the anatomic and morphological differences in glenoid bone loss (GBL) in operative patients with anterior versus posterior glenohumeral instability. METHODS: All patients over a 3-year period indicated for operative stabilization with posterior glenohumeral instability and suspected glenoid bone loss who underwent a computed tomography (CT) scan were reviewed. Included patients were then singularly matched by gender, laterality, and age (±3 years) to a collection of patients who presented for operative stabilization of anterior glenohumeral instability. GBL parameters were assessed based on the following characterizing measurements: (1) percentage of GBL, (2) glenoid vault version, (3) slope of the glenoid defect relative to the glenoid surface, (4) superior-inferior defect height, and (5) anterior-posterior defect width. RESULTS: Sixty patients (30 anterior GBL, 30 posterior GBL) were included in the final analysis (60 males), with a mean age of 28.8 ± 8.15 years (range 16.0 to 51.0 years). Patients with anterior instability presented with higher GBL (24.94% ± 7.69 vs. 9.22% ± 5.58, P < .001), greater superior-inferior defect height (23.89 ± 4.21 mm vs. 21.88 ± 3.42 mm, P = .047), and steeper slope of glenoid defect (58.80° ± 11.86 vs. 38.59° ± 14.30, P < .001), while patients with posterior instability had greater retroversion (1.53° ± 4.04 vs. 7.59° ± 7.71, P < .001). Additionally, the anterior instability cohort had significantly more patients with moderate- to high-grade glenoid bone loss (n = 30) than patients with posterior instability (n = 11) (P < .001). CONCLUSION: Anterior instability presents with a steeper slope of glenoid defect, higher percentage GBL, and greater superior-inferior defect height, whereas posterior instability presents with greater retroversion. This underscores the finding that anterior and posterior instability bone loss are not the same morphologically, and this should be considered in the operative treatment of glenohumeral instability.