Mild Valgus Alignment After Lateral Unicompartmental Knee Arthroplasty Led to Lower Functional Results and Survivorship at Mean 8-Year Follow-Up

In medial unicompartmental knee arthroplasty (UKA), the best results and the highest survivorship are found by mild undercorrection of varus deformities. In lateral UKA, the desirable amount of valgus undercorrection has not yet been determined. The purposes of this study were to present the results of a consecutive series of lateral UKAs and to investigate the effect of postoperative limb alignment on them.A total of 161 lateral UKA were reviewed. Outcomes studied included range of motion (ROM), Knee Society Score (KSS), University of California Los Angeles Activity Score, Tegner Activity Scale, Forgotten Joint Score, visual analogue scale (VAS) for pain, and survivorship. Patients were divided into two groups according to postoperative alignment: group A (hip-knee-ankle ≥184°, 79 UKA) and group B (hip-knee-ankle <184°, 82 UKA).At a mean follow-up of 8 years (range, 2-18), ROM (P < .01); KSS-C (P < .01); KSS-F (P < .01); VAS (P < .01) improved from baseline. No differences were noted in postoperative ROM, VAS, University of California Los Angeles, Tegner Activity Scale, and Forgotten Joint Score between groups. Group A showed higher postoperative clinical and functional KSS (P < .01) and higher survivorship (96.2 versus 91.5%, P = .01) than group B.Mild valgus alignment (3° or less) after lateral UKA is linked to lower clinical and functional scores and lower survivorship compared to moderate valgus (over 4°) at mean 8-year follow-up. More undercorrection of the coronal deformity in lateral UKA compared to medial UKA is desirable to get the best results.