The Impact of Anterior Glenoid Defects on Reverse Shoulder Glenoid Fixation in a Composite Scapula Model.

BACKGROUND: Achieving glenoid fixation with anterior bone loss can be challenging. Limited guidelines have been established for critical defect sizes that can be treated without supplemental bone graft when performing reverse shoulder arthroplasty.

METHODS: We quantified the impact of two sizes of anterior glenoid defects on glenoid baseplate fixation in a composite scapula using the ASTM F 2028-14 reverse shoulder glenoid loosening test method.

RESULTS: All glenoid baseplates remained well-fixed after cyclic loading in composite scapula without a defect and in scapula with an 8.5 mm anterior glenoid defect; however, one of seven baseplates loosened in a scapula with a 12.5 mm defect. No difference was observed between pre- and post-cyclic baseplate displacements in scapula with 8.5 mm or 12.5 mm defects or in the control group scapula. However, baseplate displacement in scapula with 12.5 mm anterior defects was significantly greater after cyclic loading than that of baseplates in 8.5 mm defects (superior-inferior displacement, p = 0.0004; anterior-posterior displacement, p < 0.0001), where baseplate displacement in 8.5 mm (superior- inferior displacement, p = 0.0003; anterior-posterior displacement, p = 0.0014) and 12.5 mm (superior-inferior displacement, p < 0.0001; anterior-posterior displacement, p < 0.0001) defects after cyclic loading was significantly greater than that of baseplates in scapula without a defect.

DISCUSSION: Adequate and stable fixation can be achieved in scapula with anterior glenoid defects of at least 8.5 mm in this biomechanical model using an established testing methodology; however, supplemental bone grafting should be utilized for anterior glenoid defects of 12.5 mm and larger using the reverse shoulder prosthesis tested in this study.