Mid-term outcomes of the fixed-bearing lateral Oxford unicompartmental knee arthroplasty

Mixed clinical results have been reported following the use of lateral unicompartmental knee arthroplasty (UKA) in patients with isolated lateral compartment osteoarthritis (OA) of the knee. Although this procedure may be appropriate for use in about 10% of knees needing arthroplasty, it is only used in about 1%. The aim of this study was to determine the medium-term results for the Fixed Lateral Oxford (FLO) UKA.

We report the clinical results and survival for 305 consecutive FLO UKAs implanted in 279 patients between July 2015 and August 2022. A total of 283 knees (93%) satisfied the recommended surgical indications. The mean age of the patients was 70.8 years (SD 11), their mean BMI was 28.4 kg/m² (SD 5.4), and 219 (72%) were female. Isolated lateral compartment OA was the indication for 298 operations (98%). The mean follow-up was 4.3 years (1 to 8). The Oxford Knee Score (OKS) was recorded pre- and postoperatively. The revision status of all knees was known.

There were four revisions (1%): two were conversions to a total knee arthroplasty (TKA) for instability and progressive OA and two had the addition of a medial UKA for medial compartment OA. Three other UKAs required a reoperation. At the last follow-up, the mean OKS was 40.9 (SD 7.8), a mean increase of 20 points from the preoperative score. The cumulative rate of survival with any reoperation, including revision, as the endpoint, at seven years, was 96% (95% CI 91 to 100), with revision as the endpoint was 98% (95% CI 94 to 100) and with revision to a TKA as the endpoint was 99% (95% CI 96 to 100). No revisions required revision TKA components. When those who underwent surgery for indications which were outside the recommended indications were excluded, there were only two revisions, both with the addition of a medial UKA for progressive OA, resulting in a seven-year cumulative survival with revision as the endpoint of 99% (95% CI 93 to 100).

This study involved the largest published cohort of fixed-bearing lateral UKAs. The good clinical outcomes and medium-term survival of the FLO UKA, particularly in patients satisfying the recommended indications, suggest that it is an excellent alternative to TKA for the treatment of patients with isolated OA of the lateral compartment of the knee.