60 patients with moderate knee osteoarthritis complicated with Baker's cyst were randomized in a 1:1:1 fashion to receive either horizontal therapy with aspiration and corticosteroid injection, horizontal therapy alone, or aspriation and corticosteroid injection alone. The purpose of this study was to determine the effects of horizontal therapy in cases of knee OA with secondary Baker's cyst. The results from assessments after treatment and 1 month follow-up indicated that horizontal therapy provided significant improvements in pain, stiffness and function, with even further improvement when used with concomitant aspiration and injection of corticosteroid.