Stress shielding of the proximal humerus in stemless anatomic total shoulder arthroplasty.

Background: This study aimed to assess the radiographic proximal humerus bony adaptations to stress shielding and associated clinical outcomes following stemless total shoulder arthroplasty. Methods: A retrospective review of all patients who underwent stemless total shoulder arthroplasty surgery at our centre from 2010 to 2020 was performed. Results: In total, 115 stemless total shoulder arthroplasty utilising a single implant design with a minimum one-year follow-up were identified over a 10-year period. The median follow-up was 3.5 years (range: 1-8.9 years). Evidence of stress shielding was observed in 20 cases (17%), (9 mild (8%), 0 moderate (0%), 11 severe (9%). No significant differences were seen between stress shielding and gender, body mass index, post-operative range-of-motion, patient satisfaction, or Oxford shoulder score. No significant differences were seen between the operative technique and stress shielding. No cases had evidence of humeral lucency. In total, 24 cases (21%) had evidence of glenoid lucency of Lazarus grade 0-3. No cases had Lazarus grades 4 or 5. There was no association between stress shielding and humeral lucency, glenoid lucency, or revision procedure. Discussion: Stress shielding in this study occurred at lower rates than anticipated following stemless total shoulder arthroplasty and was not associated with radiographic evidence of lucency, revision procedures, or adverse effect on clinical outcome measures.