A Flat Anterior Glenoid Corresponds to Subcritical Glenoid Bone Loss

Purpose: To define a quickly recognizable pattern for subcritical bone loss using the inflection point between the superior and inferior glenoid.

Methods: Following institutional review board approval, 3-dimensional reconstructions of 31 shoulder computed tomography scans from cadaveric specimens were obtained. Exclusion criteria were age >65 years or evidence of fracture or arthritis of the glenoid. An en face image was obtained for each glenoid. A vertical line was defined at the most anterior point of the superior glenoid. The area of the inferior glenoid anterior to this vertical line, area of the total glenoid, chord length of the anterior portion, and a best-fit circle for the inferior glenoid were measured. These numbers were compared with determine predicted bone loss relative to this vertical line. This investigation was performed at Rush University Medical Center, Chicago, IL.

Results: The mean surface area of the glenoid anterior to the vertical line was 10.2% (95% confidence interval [CI], 9.6-10.9) of the total glenoid, and 12.8% (95% CI, 12.0-13.6) of the best-fit circle of the inferior glenoid. The chord length measurement was 16.8% (95% CI, 15.7-18.3) of the total diameter of the best-fit circle. Compared with the best-fit circle, bone loss to this vertical line would represent >10% bone loss in 80.7% of patients and >13.5% bone loss in 35.5% of patients (range, 14.3%-18.1%). The negative predictive value of the vertical line was 19% for predicting 10% bone loss, 65% for predicting 13.5% bone loss, 74% for predicting 15% bone loss, and 100% for predicting 20% bone loss.

Conclusions: A flat anterior glenoid may offer a consistent pattern that corresponds to 12.8 ± 3% bone loss relative to a best-fit circle. This measurement is in line with published values of subcritical bone loss, making this a clinically useful pattern to recognize in patients with subcritical glenoid bone loss.

Clinical relevance: Our results suggest that an easily recognizable pattern of a flat anterior glenoid may correspond with more recently suggested levels of subclinical bone loss in patients with anterior shoulder instability.

Level of evidence: Level III, diagnostic study.