To investigate the effect of medial unicompartmental knee arthroplasty (UKA) on lateral compartment degeneration in medial compartment osteoarthritis of the knee.

We retrospectively analyzed 67 patients (69 knees) with medial knee osteoarthritis treated with medial mobile bearing UKA at the Orthopedic Department of Xiangyang First People's Hospital from March 2019 to March 2022. There were 14 men (14 knees) and 53 women (55 knees), and they ranged in age from 52~82 years,with a mean age of 67 years. There were 35 cases with left knee lesions, 30 cases with right knee lesions, and 2 cases with bilateral knee lesions, with a medical history of 0.5 to 10 years. The patients' intraoperative prosthesis placement angles were measured, and changes in Oxford Knee Score (OKS), Hospital for Special Surgery Knee Function Score (HSS), and Western Ontario and McMaster Universities Arthritis Index (WOMAC) before operation and at postoperative follow-up were compared, and whether the patients had painful symptoms on the lateral side of the knee, narrowing or loss of the lateral compartment joint space, and subchondral sclerosis on the frontal and lateral views of the knee was recorded. The Kellgren-Lawrance grading criteria were applied for osteoarthritis grading.

All patients were followed up for 6-36 months. At the last follow-up, the patients' HSS score and OKS score were significantly higher than those before surgery, and the OWOMAC index was significantly lower than that before surgery. In ten cases, UKA femoral prosthesis was placed in the internal reversal position, and seven patients had lateral knee pain symptoms at the follow-up, among which six showed narrowing or loss of the lateral compartment joint space on the lateral knee radiographs and subchondral sclerosis changes. UKA femoral prosthesis was placed in the standard position in 48 cases, three patients had painful symptoms in the lateral knee, but no significant changes were seen in the lateral radiographs of the knee on review. In five of these patients, the lateral radiographs of the knee showed narrowing or loss of the lateral compartment space and subchondral sclerosis.

UKA for medial compartment osteoarthritis of the knee is clinically effective in the short term, and poor intraoperative femoral prosthesis placement accelerates lateral compartment degeneration.