Arthroscopic Resection of Intra-articular Fibroma of a Tendon Sheath of the Knee: A Case Report.

Fibroma of the tendon sheath (FTS) is a benign fibrous tumor arising from the synovium of the tendon sheath and only rarely presents as an intra-articular lesion in the knee. We present a case of intra-articular FTS of the knee, successfully treated with arthroscopic excision. A 48-year-old woman presented with gradually progressive posterior knee pain for a year. On examination, the knee range of motion was limited to 0-120°, with pain elicited at both extension and flexion. Magnetic resonance imaging (MRI) demonstrated a well-defined intra-articular mass with a size of 25 × 20 × 15 mm, located posterior to the posterior cruciate ligament (PCL). The lesion was homogeneously hypointense on T1-weighted images and isointense on T2-weighted images, clearly separated from the surrounding structures. Based on these findings, an intra-articular benign tumor was suspected. Arthroscopic tumor excision was performed through a posterolateral portal. The mass was identified posterior to the PCL and resected en bloc. Histopathological examination revealed a nodular lesion composed of densely proliferating spindle-shaped cells within a collagen-rich stroma, with focal hyalinization. No cellular atypia or mitotic figures were observed. Neither multinucleated giant cells nor hemosiderin deposits were identified. Postoperatively, the patient's range of motion improved, and no recurrence has been observed at one-year follow-up. Arthroscopic excision of intra-articular FTS of the knee appears to be a safe and effective treatment. FTS should be considered in the differential diagnosis of intra-articular knee tumors. Arthroscopic excision represents a safe and effective option in such rare cases.