Isolated lateral compartment osteoarthritis of the knee (LCOA) is 10 times less frequent than medial compartment involvement. Long-term assessments of unicompartmental knee arthroplasty (UKA) in this indication are rare, with small series.

Survival and functional outcome of lateral UKA in a large series are quite acceptable; the strategy is suited for isolated LCOA.

A multicenter retrospective study in 6 French health establishments included all lateral UKAs performed between January 1988 and September 2014. Clinical data (range of motion, International Knee Society (IKS) knee and function scores, satisfaction), paraclinical data (radiologic angles) and complications were prospectively entered in medical files during follow-up and analyzed retrospectively at end of follow-up.

During the study period, 311 lateral UKAs were performed in 295 patients, using 5 fixed-bearing implant models. Twenty-eight patients died within 5 years, and 15 (4.8%) were lost to follow-up. The series thus comprised 268 lateral UKAs in 63 male and 205 female patients, with a mean age of 68.8±10.5 years, including 7 cases of post-traumatic osteoarthritis and 4 of aseptic osteonecrosis. Mean follow-up was 9.1 years (range, 5-23 years), implant survivorship with failure defined as all-cause revision surgery was 85.4% at 10 years and 79.4% at 20 years. At last follow-up, IKS knee score was 87.0 and IKS function score 80.2. Maximal flexion was 125°. 94.3% of patients were satisfied or very satisfied. The main cause of revision surgery was osteoarthritis in another knee compartment (66,7%, n=26).

Lateral UKA showed good survivorship, comparable to medial UKA, with good functional results and excellent long-term satisfaction.

IV, retrospective cohort study.