Arthroscopic Capsular Release for Refractory Frozen Shoulder after COVID-19 Vaccination:A Report of Two Cases

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Background:Shoulder injury related to vaccine administration (SIRVA) has been discussed as a complication of incorrect intramuscular vaccination technique, resulting in subacromial/subdeltoid bursitis or injury of the anterior branch of the axillary or radial nerve. Case presentation:We have encountered two cases of frozen shoulder following COVID-19 vaccination. In both cases, arthroscopic capsular release was performed after failure of conservative treatment. Arthroscopy revealed severe synovitis in the glenohumeral joint characteristic of idiopathic frozen shoulder. Conclusions:In these two cases, the synovial inflammation was predominantly intra-articular, suggesting that the pathology of frozen shoulder secondary to SIRVA was different from that reported previously. Although the postoperative course was favorable in these two cases, early diagnosis and prompt therapeutic intervention are essential to prevent development of frozen shoulder after COVID-19 vaccination. J. Med. Invest. 72 : 459-462, August, 2025