Large variance in a lateral osteoarthritic population prior to and following lateral unicompartmental arthroplasty: An analysis of knee phenotypes.

ABSTRACT

BACKGROUND: Disagreement exists on the optimal coronal alignment target for lateral unicompartmental knee arthroplasty (UKA). An improved understanding of the distribution of coronal alignment and joint line orientation in lateral osteoarthritis (OA) might prove beneficial. The aim of this study was to evaluate the pre- and postoperative Coronal Plane Alignment of the Knee (CPAK) distribution following lateral UKA and to evaluate the association between phenotypic variation and patient-reported outcome measures (PROMs). METHODS: A surgeon's registry was retrospectively reviewed between 2012 and 2022 to identify patients who received primary lateral UKA for advanced, lateral compartment OA. Radiographic measurements were performed, and CPAK phenotypes were determined. The Knee Injury and Osteoarthritis Outcome Score (KOOS), Kujala, and patient satisfaction were analyzed at one-year and two-year follow-up. RESULTS: A total of 305 knees were included. Preoperatively, seven phenotypes were observed and CPAK3 (54.1%) was most commonly observed. Postoperatively, all nine phenotypes were observed and CPAK6 (32.8%) was predominant. Preoperatively, 23.6% did not have a prearthritic valgus alignment. No significant differences in PROMs were found between individual phenotypes or between preserved and altered phenotypes. CONCLUSION: Coronal alignment and joint line orientation were highly variable within a lateral compartment OA cohort. However, no association was demonstrated between superior postoperative PROMs and phenotype variation or phenotype preservation, which might suggest that there is not one universal optimal alignment target. Interestingly, 23.6% of knees with lateral compartment OA did not have a prearthritic valgus alignment, which may have been affected by joint line orientation.