How are clinical outcomes related to the deviation severity of the tibiofemoral mechanical axis on coronal plane following knee arthroplasty

Abstract Objective To analyze the effect of tibiofemoral mechanical axis (TFMA) deviation severity on clinical outcomes after total knee arthroplasty (TKA). Methods We retrospectively reviewed the patients who underwent primary TKA between January 2002 and December 2010. After applying inclusion/exclusion criteria, we evaluated 70 knees of 51 patients. The mean ± SD follow-up period was 7.08 ± 1.34 years. The knees were divided into 3 groups based on TFMAs. The first group, identified as “well aligned,” included the TFMAs that were neutral within 3° (0° ± 3°) of alignment. The second group, identified as “outliers 1,” included the slightly deviated TFMAs (−3° to −6° valgus and +3° to +6° varus). The third group, identified as “outliers 2,” included the severely deviated TFMAs of more than 6° from neutral alignment (  + 6° varus). The clinical outcomes of each group were compared by evaluating the Oxford Knee Score (OKS), visual analog scale (VAS), and Short Form-36 physical component summary (SF-36 PCS) and mental component summary (SF-36 MCS) scores. Results We found that OKS, SF-36 PCS, and SF-36 MCS were nearly the same in the well-aligned and outliers 1 groups but worse in the outliers 2 group. VAS scores were nearly the same in all groups. ( p >  0.05) Conclusion Function scores were impaired when the TFMA deviated more than 6° from neutral. However, the differences in clinical outcomes between well-aligned knees and those of outliers were not found to be statistically significant in the medium term.