Biomechanical analysis of anterior bone graft augmentation with reversed shoulder arthroplasty in large combined glenoid defects compared with total bony joint line reconstruction (modified bony-increased-offset reversed shoulder arthroplasty).

BACKGROUND: The aim of this biomechanical study was to compare 2 surgical techniques for the reconstruction of large, combined, uncontained glenoid defects with reversed shoulder arthroplasty (RSA).

METHODS: Three groups of scapulae with RSA were tested by the application of a physiological combination of compressive/shear loads in Sawbones (Pacific Research Laboratories, Inc., Vashon Island, WA, USA) and cadavers. Two of the groups (both Sawbones and cadaveric specimens) consisted of anterior combined defects (14 mm in depth), and the third group served as a control group (only Sawbones specimens). The first group with an anterior combined defect was reconstructed with anterior bone grafts to contain the defect and cancellous bone to fill the central defect before RSA with partial bony joint line reconstruction (p-BJR). In the second group with an anterior combined defect, the dorsal rim was reamed and the joint line was reconstructed with a bone disc fully covering the peg. This total BJR (t-BJR) corresponds to the technique of bony-increased-offset-RSA (BIO-RSA).

RESULTS: At 150 µm of displacement, the loadings in the inferior-superior (IS) direction were significantly more stable than those in the anterior-to-posterior (AP) direction within both reconstructed defect groups (P ≤ .002). In contrast, no significant differences were found between the partial BJR and t-BJR group in either direction (Sawbones: AP: P = .29; IS: P = .44; cadavers: AP: P = .67; IS: P = .99). The control group revealed significantly higher values in all loadings of the IS direction and significantly higher loadings at 40 µm and 150 µm in the AP direction.

CONCLUSION: Both techniques could be applied for such complex defects provided that there is sufficient medial bone stock for a t-BJR. Significantly greater stability was found in the IS direction than in the AP direction within each group, which could be explained by the longer screw anchoring within the superior and inferior columns. Both defect groups were less stable than the group of intact glenoids.