Kinematically aligned total knee arthroplasty is as effective in severe varus deformities as in mild deformities.

Purpose: This study compares the clinical outcomes and radiological measures of kinematic alignment total knee arthroplasty (KA-TKA) in patients with severe knee deformities to those with mild varus.

Methods: This retrospective cohort study included 145 patients with <10° varus malalignment and 145 patients with >10° varus. All cases underwent KA-TKA performed by a single surgeon using the same techniques between 2015 and 2022. The following variables were compared between groups: (1) demographic data, (2) clinical assessments including ROM, pre- and postoperative Oxford knee score (OKS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), as well as postoperative knee society score (KSS) and forgotten joint score (FJS) and (3) radiographic parameters including femoral mechanical angle (FMA), tibial mechanical angle (TMA) and hip-knee-ankle (HKA). All postoperative data were collected after 2-9 years of follow-up (median: 6 years).

Results: Preoperative parameters, including age, sex, height, weight, body mass index (BMI) and side of operation, were not significantly different between groups. Preoperative WOMAC and Oxford knee score (OKS) scores were significantly worse in the severe group (p < 0.001). However, both scores improved significantly more in the severe varus knees postoperatively. Postoperative KSS (mild: 87.31 ± 14.35 vs. severe: 83.79 ± 24.82, p = 0.93) and FJS (mild: 91.83 ± 8.09 vs. severe: 91.38 ± 12.16, p = 0.23) did not show significant differences. Though pre- and postoperative ROMs were significantly lower in the severe group (p < 0.001), they improved significantly in both groups without significant difference (p = 0.16). Preoperative HKA was 173.85 ± 1.79 degrees in the mild group and 159.83 ± 7.59 degrees in the severe group (p < 0.001). There was also a significant difference in preoperative FMA (p < 0.001) and TMA (p = 0.003) between groups. KA-TKA corrected HKA (13.44 ± 5.78 vs. 3.92 ± 2.36) and TMA (6.19 ± 5.41 vs. 2.10 ± 3.26) significantly more in patients with severe varus knee (p < 0.001).

Conclusion: KA-TKA enhances clinical outcomes in individuals with severe knee varus to a degree comparable to those with mild varus. This technique achieves a more profound correction of HKA alignment in severe cases than in mild cases. KA-TKA may be a viable approach, but further prospective comparative studies are needed, especially in patients with severe deformities.

Level of evidence: Level III.