Forty patients with medial compartment knee osteoarthritis (OA) who previously underwent high tibial osteotomy (HTO) were randomized to investigate the effect of adding two courses of intra-articular hyaluronic acid injections to postoperative care. Patients received either HA injections or no treatment, and were monitored over the course of 1 year with regards to cartilage volume and functional outcomes. The results of this study indicated significant improvement in cartilage volume, lateral femoral cartilage, and lateral tibial cartilage for patients treated with HA, as compared to the control. Cartilage volume loss was noted at the lateral tibial plateau in the control group. WOMAC significantly and similarly improved in both groups, while HA patients used significantly lower amounts of rescue medication.