This study's aim was to determine the patterns of osteoarthritis (OA) in both unicompartmental medial and lateral OA of the knee. Forty patients with medial and 20 with lateral unicompartmental knee osteoarthritis were studied to determine the location of full-thickness cartilage lesions. Intraoperatively, the distance between margins of the lesion and reference lines were measured. The femoral measurements were transposed onto lateral radiographs to determine the relationship between the lesion site and knee flexion angles. Both tibial and femoral lesions were significantly (p