Cysts and other masses about the knee: identifying and treating common and rare lesions.

Masses about the knee are most commonly benign cysts. The diagnosis can often be made with a history and physical exam, but radiographs and MRI are sometimes required, and histologic evaluation is occasionally necessary. Popliteal (Baker's) cysts are often indicative of arthritis; treatment for the underlying pathology may reduce swelling and permit resorption. Meniscal cysts indicate an underlying tear; treatment is resection and cyst excision. Symptomatic ganglion cysts generally require surgical excision. Treatment for bursitis is conservative. The less-common synovial chondromatosis, pigmented villonodular synovitis, synovial sarcoma, and lesions of the proximal tibiofibular joint generally require referral and surgery.