Impact of knee varus and valgus deformity on alignment in lower extremities after total knee arthroplasty (TKA).

OBJECTIVE: To investigate the impact of knee varus and valgus in varying degrees on the alignment in lower extremities of patients who received the total knee arthroplasty (TKA).

PATIENTS AND METHODS: We retrospectively analyzed the condition of varus and valgus deformity in full-length X-ray films of double lower extremities in weight-bearing position of 120 patients before and after they firstly received the TKA between March 2012 and May 2014 to discover the impact of knee varus and valgus in varying degrees on the alignment in lower extremities of patients who received the total knee arthroplasty (TKA). 120 patients were divided into three groups by the pre-operative hip-knee-ankle angle (HKA), the HKAs of three groups were compared after operation, and linear regression analysis was conducted to identify the correlation between pre- and post-operative HKAs. In addition, comparison between the pre- and post-operative lean of arms and legs (LMAL) was carried out to explore the variations before and after operation as well as the differences in the average variations among three groups.

RESULTS: The differences were statistically significant in comparison of the pre- and post-operative HKAs and medial proximal tibia angles (MPTA) of all affected extremities (p<0.05), but no statistically significant difference was shown in comparison between the pre- and post-operative knee physical valgus angles (KPVA) (p>0.05). The post-operative lengths of 86.57% of affected extremities (116/134) were longer than those before operation with statistically significant differences (p<0.05). However, no statistically significant difference was identified in comparison between the pre- and post-operative lengths of extremities that did not receive any operation (p>0.05). The ratios of HKAs between -3° and 3° in normal group, mild-deformity group and severe-deformity group were respectively 90.48%, 81.25%, and 34.69% with a statistically significant difference (p<0.05). Besides, the scatter plot revealed that there was a linear regression relation between pre- and post-operative HKAs (F=51.197, p<0.05). There were statistically significant differences in comparisons of the pre-operative KPVA and MPTAs among three groups (p<0.05).

CONCLUSIONS: Severe knee varus and valgus deformity can increase the deviation of alignment in lower extremities after TKA, and most of LMALs after TKA are longer than those before TKA, and the most significant extension is identified in severe varus and valgus deformity.