Ultrasonographic assessment of Baker's cysts after intra-articular corticosteroid injection in knee osteoarthritis

PURPOSE: To assess sonographic changes in Baker's cysts (BCs) of patients with knee osteoarthritis after a single intra-articular corticosteroid injection. METHODS: Thirty patients with knee osteoarthritis complicated with a symptomatic BC received a single intra-articular injection of 40 mg triamcinolone acetonide. Knee pain, swelling, and range of motion were evaluated. BC area and thickness of the cyst wall were measured with sonography before and 4 weeks after local treatment. RESULTS: A significant improvement in knee pain, swelling, and range of motion after corticosteroid injection was accompanied by a decrease in size of the BCs as well as in thickness of the cyst wall as measured by sonography. Moreover, the reduction of BC area on sagittal scans after treatment was significantly correlated with the improvement in range of motion. CONCLUSIONS: In this series of osteoarthritis patients, injection of corticosteroids inside the knee joint accounted for a reduction in BC dimensions as well as cyst wall thickness. Sonography can be used not only for the diagnosis of BCs but also to monitor response to therapy.