Functional Outcomes of Residual Varus Alignment Versus Mechanical Alignment in Total Knee Arthroplasty for Varus Osteoarthritis: A Preferred Reporting Items for Systematic Reviews and Meta-Analyses-compliant Meta-Analysis

Background One in five patients with mechanical alignment (MA) after total knee arthroplasty (TKA) was reportedly dissatisfied. As constitutional varus knees are common, restoring the patients’ natural residual varus (RV) alignment is as an appealing alternative to neutral MA. This meta-analysis aimed to evaluate the effects of RV alignment on the functional outcomes compared with those of MA in TKA for the knees with varus osteoarthritis. Methods The MEDLINE/PubMed, Cochrane Library, and EMBASE databases were comprehensively searched for papers comparing the effects of RV alignment and MA on the functional outcomes from the time of inception of the databases to July 2020. Studies comparing the functional outcomes in the knees subjected to TKA with RV alignment (case group) and MA (control group) were included. The Knee Society knee and functional scores (KSKS and KSFS, respectively), Western Ontario and McMaster University Osteoarthritis Index (WOMAC), Oxford knee score (OKS), and forgotten joint score (FJS) were compared. Results Seven studies were finally included; all studies showed a low risk of selection bias and provided detailed demographic data. The pooled mean difference in the KSKS (0.06, 95% confidence interval [CI]: −0.14 to 0.27; p = 0.55) and KSFS (0.08, 95% CI: −0.08 to 0.35; p = 0.56) between RV alignment and MA did not significantly differ. The pooled mean differences in the WOMAC (−0.25, 95% CI: −0.57 to 0.07; p = 0.12), OKS (0.06, 95% CI: −0.15 to 0.27; p = 0.56), and FJS (0.41, 95% CI: −0.18 to 1.00; p = 0.18) between the groups were not significant. Conclusion The beneficial effects of RV alignment on the functional outcomes are limited compared to those of MA in TKA for varus osteoarthritis to date. Currently, TKA with neutral MA should be considered as the gold standard.