Early results of fixed-bearing unicompartmental knee replacement designed for the lateral compartment

Background Isolated lateral compartment knee arthritis is less prevalent than medial. While the reported results of medial unicompartmental knee replacement (UKR) have been good and comparable to total knee replacement, the results of lateral UKR have been mixed. We present the short-term results and survivorship of a fixed-bearing UKR designed specifically for the lateral compartment. Methods We report the result of 130 primary fixed-bearing lateral Oxford (FLO) UKRs (123 patients) performed between 2015 and 2019 with a minimum follow-up of 1 year. The indications for lateral UKR were: isolated lateral osteoarthritis (n = 122), post-trauma (n = 5) and osteonecrosis (n = 3). The mean age was 69.1 (+/- 11.6), mean BMI 28.4 (+/- 4.9), 66.9% female, 60% right-sided, and mean follow-up 3 (range 1-4.8 years, standard deviation +/- 1) years. The primary outcome measure was the Oxford knee score (OKS). Survival analysis was performed with "revision for any reason", "reoperation", and "implant failure" as the endpoints. Results Six patients died from unrelated reasons. None of the implants failed. One required the addition of a medial UKR for medial arthritis. There were no other reoperations. At 4 years, the survival for implant failure was 100% and for both revision and all reoperations was 99.5% (95% CI 96.7-99.9%). At the last review, at a mean of 3 years, the mean Oxford knee score was 41. Conclusion The good survivorship and outcome scores suggest that UKR designed for the lateral compartment is an excellent alternative to total knee replacement in selected patients with isolated lateral tibiofemoral arthritis at short-term follow-up.