How does anterior glenoid bone loss affect shoulder stability? A cadaveric analysis of glenoid concavity and bony shoulder stability ratio.

Abstract

Concavity compression is an important glenohumeral stabilizing factor, and recent studies have suggested that peripheral glenoid bone loss creates the most relevant change in stability. This study analyzed changes in the bony shoulder stability ratio (BSSR) with sequential anterior glenoid bone loss (0%-40% width) and with reconstructive bone graft procedures. The aim was to quantify the critical bone defect size that would significantly alter the BSSR and determine restoration of the BSSR with the Latarjet procedure. Anterior glenoid defects were created with sequential osteotomies (10%-40%), and defects were reconstructed using 2 Latarjet modifications (classic Latarjet procedure and congruent-arc Latarjet [CAL] procedure). We obtained 108 computed tomography scans of (1) intact scapulae (n = 12), (2) after each bone defect (n = 48), and (3) after each reconstruction (n = 48). The glenoid concavity depth and concavity radius were measured, and the BSSR was determined using a validated mathematical formula. Statistical analysis was performed to determine significant differences between the intact state and each of the deficient and reconstructed glenoids. The glenoid concavity radius increased by approximately 30% (14 mm) and the glenoid concavity depth decreased by 50% (1.5 mm) from the 0% to 40% defect. The maximal sequential change in depth (1.2 mm, 44%; P < .001) and radius (6 mm, 12%; P < .001) occurred at the 10% glenoid defect. The overall BSSR decreased by approximately 40% (0.15) from the intact glenoid to the 40% defect. This change in the BSSR was most profound (0.11, 30%; P < .001) at the 10% glenoid defect and was only marginal thereafter between the 20% and 40% defects (0.24, 0.22, and 0.21). The Latarjet procedure adequately restored glenoid concavity; however, the CAL procedure significantly overcorrected all 3 parameters at 10% defect. The glenoid concavity depth and BSSR undergo progressive deformation with sequential bone loss, and 90% of this change occurs with a 10% glenoid defect. Articular concavity and the BSSR are adequately restored with the Latarjet procedure, and the CAL procedure significantly overcorrects concavity in mild (0%-10%) defects.