Excellent Implant Survivorship and Knee Function of a Fixed Lateral Unicompartmental Knee Arthroplasty: A Consecutive Single-Center Series of 1,015 Knees at a Mean Follow-Up of Five Years.

BACKGROUND

Isolated lateral-compartment knee osteoarthritis (OA) remains a condition challenging to treat. Lateral unicompartmental knee arthroplasty (UKA) may offer therapeutic advantages over total knee arthroplasty (TKA); however, it remains infrequently performed. This study determined implant survivorship and reoperation-free survival in a consecutive single-center series of primary lateral UKA. Furthermore, patient-reported outcome measures (PROMs) and radiological outcomes were assessed.

METHODS

In this retrospective analysis, 1,015 knees in 927 patients (75% women) who had a mean follow-up of 5.1 years (range, 2.0 to 8.9) were included (mean age 70 years, range, 37 to 94; mean body mass index 27.5, range, 15 to 48). All patients were contacted via telephone to record implant survivorship, any reoperation, and the functional outcome (follow-up rate: 92%). Preoperative and postoperative radiographs were obtained following a standardized protocol. The Oxford Knee Score and the University of California, Los Angeles Activity Score were documented. Patients who had a previous ipsilateral medial UKA or patellofemoral arthroplasty and patients who declined consent were retrospectively excluded. Cumulative survival was calculated using Kaplan-Meier survival analysis.

RESULTS

The cumulative 9-year survival rate was 97.6% (95% confidence interval: 96.6 to 98.6) with implant revision as the endpoint and 92.4% (95% confidence interval: 90.4 to 94.4) with reoperation for any reason as the end point. Medial-compartment OA progression was the most common reason for reoperation (2.8%), followed by medial osteonecrosis (1.1%) and infection (0.8%). The mean Oxford Knee Score improved from 23.9 ± 8.0 to 43.2 ± 6.4 (P < 0.001); the mean University of California, Los Angeles Activity Score improved from 4.5 ± 1.7 to 5.8 ± 1.6 (P < 0.001). The mean hip-knee-ankle angle was corrected from 7.4° ± 4.5 valgus to 2.4° ± 2.6 valgus (P < 0.001).

CONCLUSIONS

This study demonstrated that primary lateral UKA is a highly successful procedure with excellent implant survival and favorable PROMs at a mean follow-up of five years. The low revision rates and promising functional outcomes strongly confirm its role as a viable alternative to TKA in appropriately selected patients who have isolated lateral-compartment OA.

LEVEL OF EVIDENCE: IV, case series.