Influence of the post-operative axis on the clinical results of total knee replacement for severe varus deformities: does a slight residual varus improve the results?

Purpose

Some recent articles have suggested that in the case of large varus deformity, it may be advantageous to leave some residual post-operative varus as a means of improving functional outcome.

The objective of this study is to compare the results of total knee replacement (TKR) performed for significant varus deformity (HKA < 170°) where there is a residual post-operative varus (HKA < 180°) to the results of TKR for significant varus deformity with either neutral post-operative (HKA = 180°) or mild valgus post-operative alignment (HKA > 180°).

Methods

This series was made up of 208 knees. The mean pre-operative HKA angle was 166 ± 3° (154–169°), of which 150 were followed up for a mean 8.5 years (58 lost to follow-up). Based on post-operative radiographs, two groups were formed: group 1 (88 knees) in which post-operative alignment was 177.8 ± 1° (175–179°) and group 2 (62 knees) in which post-operative alignment was 181 ± 1° (180–184°).

Results

The mean international knee society (IKS) score for group 1 was 178.8 ± 22 points (113–200) and 181.7 ± 22 points (95–200) for group 2. Oxford knee score was 20.4 ± 9 points (12–45) in group 1 and 19.2 ± 9 (12–50) in group 2. The results were slightly better in group 2 (in slight valgus) but this difference was not statistically significant (p = 0.44 and 0.4).

Conclusion

The results of knee replacement performed for severe varus deformity are not adversely affected by post-operative valgus alignment. There is in fact a trend towards superior results for neutral or valgus alignment than slight residual varus, but this difference was not statistically significant.