Localized nodular synovitis of the knee presenting as anterior knee pain: a case report.

The localized nodular synovitis is a benign proliferative synovial tumor manifesting as an intra-articular solitary nodule. We report a case of localized nodular synovitis at the infrapatellar fat pad of the knee which presented as a vague symptom of anterior knee pain. An arthroscopic excision of the lesion relieved the anterior knee pain and there has been no evidence of recurrence. Although the localized nodular synovitis shares some common histologic features with the pigmented villonodular synovitis without villous fronds, hemorrhage, or hemosiderin deposit, it is important to make a distinction between the two entities because their clinical presentations differ greatly, as do their responses to treatment. This rare tumorous lesion should be included in the differential diagnosis of common clinical symptom of anterior knee pain.