Characterization of Posterior Glenoid Bone Loss Morphology in Patients With Posterior Shoulder Instability.

PURPOSE:To systemically describe posterior bone defects in the setting of posterior shoulder instability based on several parameters, including surface area, slope and version, defect height from the base of the glenoid, and extent of bone loss at equal intervals along the long axis of the fossa. METHODS:A total of 40 young, active individuals with recurrent posterior shoulder instability and a bony injury confirmed on either computed tomography (n = 18; mean age, 26.3 ± 4.0 years) or magnetic resonance imaging (n = 22; mean age, 20.0 ± 4.9 years) were identified. The posterior glenoid bone defect was characterized using the following measures: (1) percentage of bone loss, (2) glenoid vault version, (3) slope of the posterior defect relative to the glenoid surface, (4) superior-inferior length of the defect, and (5) anterior-posterior width of the defect at 5 intervals along the glenoid fossa. RESULTS:The mean age of the 40 patients was 22.9 ± 5.5 years (range, 14.9-35.5 years). The mean surface area of glenoid bone loss was 9.7% ± 4.7%. Glenoid version measured at 5 equal intervals along the inferior two-thirds of the glenoid was 12.8° ± 4.9°, 11.9° ± 5.0°, 10.1° ± 6.3°, 10.5° ± 6.5°, and 8.7° ± 7.2° from superior to inferior. The mean slope of the posterior defect relative to the glenoid fossa was 26.8° ± 11.5°. The mean superior-inferior height of the bony defect was 21.9 ± 0.4 mm. The anterior-posterior sloped width of the defect at 5 equal intervals along the glenoid fossa was 0.9 ± 1.5 mm, 2.8 ± 2.4 mm, 4.0 ± 1.7 mm, 4.0 ± 2.1 mm, and 2.9 ± 2.6 mm from superior to inferior. Low-grade (<10%) bone loss was diagnosed in most shoulders (23 of 40 evaluated), whereas 15 had moderate bone loss (10% to <20%) and 2 had high-grade bone loss (≥20%). CONCLUSIONS:Posterior glenoid bone loss is characterized by a loss of posterior bony concavity, increased slope from anterior to posterior, and increased posterior version. The most anterior-posterior sloped width was quantified at the third and fourth intervals of 5 equal intervals from superior to inferior. This study highlights that patients with posterior instability have bone loss that is sloped relative to the glenoid fossa and suggests that management must be appropriately tailored given the distinctiveness of posterior bone loss. LEVEL OF EVIDENCE:Level IV, case series.