Loose Body Formation in the Subacromial Bursa following Rotator Cuff Repair with a REGENETEN® Bioinductive Implant: A Case Report.

Introduction: The REGENETEN® bioinductive collagen implant (Smith and Nephew, Andover, MA) has been increasingly used in rotator cuff repair as a biological scaffold to promote tendon regeneration. Clinical studies have shown favorable healing and reduced retear rates, with complications considered rare. We present a rare case of loose body formation within the subacromial bursa following rotator cuff repair with REGENETEN®. Case Report: A 60-year-old man presented with the right shoulder pain. Magnetic resonance imaging (MRI) revealed a partial-thickness tear of the supraspinatus tendon, and conservative treatment was initiated. Due to persistent nocturnal pain, arthroscopic repair was performed 3 months later using a medium-sized REGENETEN® implant secured on the tendon surface. Postoperatively, passive range-of-motion exercises began at 2 weeks, and active exercises at 3 weeks. At 6 weeks, the patient developed recurrent shoulder pain and mechanical catching. Despite continued rehabilitation, symptoms worsened. At 6 months, MRI demonstrated a hypointense structure within the subacromial bursa. Diagnostic arthroscopy revealed a whitish, mobile loose body measuring 16 × 13 mm, containing a medial implant staple encapsulated by fibrous tissue, while the repair site remained intact. The loose body was excised arthroscopically. Histological examination demonstrated fibrin deposition, infarcted necrotic fibrous tissue, and fibrocollagenous proliferation, findings consistent with a foreign body reaction. The post-operative course was uneventful, symptoms resolved within 1 month, and the patient returned to full occupational activity within 2 months. Conclusion: Although REGENETEN® has been proven safe and effective, rare complications such as implant detachment and foreign body reactions should be considered. Unlike rice body formation, which is associated with systemic inflammatory conditions and necessitates evaluation for underlying rheumatologic disease, the present case represents an implant-derived loose body that was definitively treated by surgical excision. To the best of our knowledge, this is a rare case of loose body formation within the subacromial bursa due to migration of a REGENETEN® implant staple. Awareness of this complication is clinically important in patients with persistent post-operative mechanical symptoms following rotator cuff repair with REGENETEN®.