Synchronous Intra-Articular Osteochondroma and Reactive Synovitis Mimicking Diffuse Tenosynovial Giant Cell Tumor of the Knee: A Case Report
Nicolás Mcallister1, Emilio López Avella1, Maria Antonia Ramirez1, Francisco Bernardo Linares Restrepo1*
1Departments of Orthopaedics and Traumatology, Hospital Universitario San Ignacio, Pontificia Universidad Javeriana Faculty of Medicine, Bogotá, Colombia.
*Corresponding Author: Francisco Bernardo Linares Restrepo, Departments of Orthopaedics and Traumatology, Hospital Universitario San Ignacio, Pontificia Universidad Javeriana Faculty of Medicine, Bogotá, Colombia.
https://doi.org/10.58624/SVOAOR.2026.06.030
Received: July 27, 2026
Published: October 16, 2026
Citation: Mcallister N, López Avella E, Ramirez MA, Linares Restrepo FB. Synchronous Intra-Articular Osteochondroma and Reactive Synovitis Mimicking Diffuse Tenosynovial Giant Cell Tumor of the Knee: A Case Report. SVOA Orthopaedics 2026, 6:5, 226-234. doi: 10.58624/SVOAOR.2026.06.030
Abstract
Introduction: True intra-articular osteochondroma of the knee arising from the femoral condyle is exceptionally rare, and to our knowledge its coexistence with a synovial lesion that macroscopically mimics diffuse tenosynovial giant cell tumor (TGCT) has not been previously reported.
Case presentation: We describe a 59-year-old woman with a two-year history of right knee pain and a progressively enlarging soft-tissue mass that had been attributed to osteoarthritis. Magnetic resonance imaging showed an exophytic osteocartilaginous lesion of the anterior medial femoral condyle, together with a heterogeneous intra-articular effusion with fluid-fluid levels and synovial thickening. After review by the oncologic tumor board, the patient underwent excisional resection with synovial margins. Two grossly distinct lesions were found at surgery: a synovial lesion with a macroscopic appearance suggestive of TGCT, and a separate intra-articular osteocartilaginous lesion. Histopathology showed reactive synovitis with old hemorrhage and no malignant component, and a benign osteocartilaginous lesion most compatible with osteochondroma, with a 5 mm cartilage cap. Her early postoperative course showed gradual functional recovery consistent with expected timelines after extensive synovectomy. Conclusion: This case illustrates two points relevant to clinical practice: the potential for reactive, hemorrhagic synovitis to mimic TGCT macroscopically, and an oncologic decision-making approach for intra articular lesions in which preoperative cartilage-cap measurement and biopsy are unreliable or risk violating tumor margins.
Keywords: Osteochondroma; Tenosynovial Giant Cell Tumor; Synovitis; Knee Joint; Diagnosis, Differential; Case Report