Arthroscopic one-stage management of diffuse shoulder pigmented villonodular synovitis with concomitant full-thickness rotator cuff tear and acromial bone erosion: a rare case report.

The coexistence of diffuse shoulder pigmented villonodular synovitis (PVNS), full-thickness rotator cuff tear, and PVNS-induced focal acromial bone erosion is extremely rare, with no prior reports documenting this complete pathological triad, which poses unique diagnostic and therapeutic challenges. We report a 52-year-old male with a three-month history of progressive right shoulder pain, swelling, and functional limitation. Radiographs showed cortical irregularity of the acromion, while MRI revealed extensive synovial proliferation with low signal on T1/T2 sequences, suggestive of PVNS, and a full-thickness supraspinatus tendon tear. The patient underwent single-stage arthroscopic synovectomy, rotator cuff repair using a double-row suture bridge technique, and debridement of a small acromial bone defect. Histopathology confirmed diffuse-type PVNS. Preoperative ASES and VAS scores were 38.2 and 6, respectively, improving to 75.8 and 2 at three months, and to 92.5 and 1 at five months post-surgery, with satisfactory early functional recovery. This case highlights that PVNS should be included in the differential diagnosis of persistent shoulder monoarthritis, even in patients with typical rotator cuff tear signs, especially when accompanied by atypical bone lesions on imaging. One-stage combined arthroscopic complete synovectomy, anatomical rotator cuff repair, and bone erosion debridement is a feasible and effective minimally invasive strategy for managing this complex pathological combination. The early clinical outcomes are encouraging, however, given the short follow-up, these early outcomes should be interpreted cautiously, and long-term surveillance is required.