A 57-yr-old female with a history of C4-ASIA-D tetraplegia presented with a single transient episode of right-knee locking. She denied having any such episodes in the past. Three months before, she had presented to her primary care physician with a sudden onset of right-knee swelling. There was no apparent trigger and no associated pain, and her swelling resolved with “over-the-counter” anti-inflammatory medications. Before these events, she had noted an insidious onset of increasing difficulty with the right-knee range of motion and ambulation but had attributed this to her right lower limb spasticity, which was being treated with oral baclofen.
Upon physical examination of the right lower limb, strength and spasticity was unchanged from previous visits. She continued to use a right-molded ankle foot orthosis and ambulated using a straight cane without difficulty. There was no joint effusion and only a mild decrease in the range of motion.
Magnetic resonance imaging of the right knee revealed a multilobulated mass of the posterior aspect of Hoffa’s fat pad, measuring 2.6 × 1.0 × 1.8 cm (Fig. 1), which is highly suggestive of pigmented villonodular synovitis (PVNS). Arthroscopic resection revealed that the PVNS was larger than initially seen on the magnetic resonance image, measuring more than 7 cm and seemingly encompassing a large portion of the knee joint. Immediately after surgery, she noted significant improvement in the range of motion and a course of physical therapy restored her gait pattern and previous level of ambulation and activity.
PVNS is a rare benign proliferation of the synovium that presents as a slow-growing giant cell tumor of unknown etiology and can imitate many other conditions including synovial chondromatosis and hemophiliac arthropathy.1,2 Common clinical presentation includes joint locking and/or a sudden onset of swelling out of proportion to pain.2 Its incidence is approximately 1.8 in one million and presents as a monoarthritis involving the knee in 80% of cases but can also involve the hip, ankle or shoulder.1 Although PVNS can be diagnosed through magnetic resonance imaging, definitive diagnosis is established through synovial biopsy.1 Treatment of localized PVNS after diagnosis is done through open or arthroscopic excision and has a good prognosis.3
1. Frassica FJ, Bhimani MA, Mccarthy EF, et al.: Pigmented villonodular synovitis of the hip and knee. Am Fam Physician 1999; 60: 1404–15
2. Flandry F, Hughston JC, McCann SB, et al.: Diagnostic features of diffuse pigmented villonodular synovitis of the knee. Clin Orthop 1994; 298: 212–20
3. Kramer DE, Frassica FJ, Frassica DA, et al.: Pigmented villonodular synovitis of the knee: Diagnosis and treatment. J Knee Surg 2009; 22: 243–54