ステムless reverse total shoulder arthroplastyへの変換、持続的な肩不安定症患者におけるステムless 解剖学的インプラントの転位後：症例報告

Stemless anatomic total shoulder arthroplasty (aTSA) offers bone preservation advantages in younger patients, but postoperative instability requiring revision to reverse total shoulder arthroplasty (rTSA) occurs in 20%-32% of cases, representing a major indication for revision surgery. Although stemless rTSA has demonstrated promising early outcomes in Europe since 2005, it remains investigational and not Food and Drug Administration-approved in the United States. We report a 54-year-old female who developed implant dislocation and subscapularis tendon failure 8 weeks after primary stemless aTSA (Sidus system, Zimmer Biomet) for primary glenohumeral osteoarthritis. Given the well-fixed, convertible stemless humeral component and adequate metaphyseal bone quality, off-label conversion to stemless rTSA was performed with component retention. This approach is aimed at preserving proximal humeral bone stock, reducing operative time and blood loss, and potentially decreasing infection risk. At 2-year follow-up, the patient demonstrated excellent functional outcomes, improved range of motion, and stable radiographic findings. To our knowledge, this is the first report describing clinical and radiographic outcomes following revision of a dislocated stemless anatomic shoulder implant to a stemless reverse configuration.