Hip-Knee-Ankle (HKA) angle modification during gait in healthy subjects

Background: Achieving a neutral static Hip-Knee-Ankle angle (sHKA) measured on radiographs has been considered a factor of success for total knee arthroplasty (TKA). However, recent studies have shown that sHKA seems to have no effect on TKA survivorship. sHKA is not representative of the dynamic loading occurring during gait, unlike the dynamic HKA (dHKA). Research question: The primary objective was to see if the sHKA is predictive of the dynamic HKA (dHKA). A secondary objective was to document to what degree the dHKA changes during gait. Methods: We analysed 3D knee kinematics during gait of a cohort of 90 healthy individuals with the KneeKG (TM) system. dHKA was calculated and compared with sHKA. Knees were considered "Stable" if the dHKA remained in valgus or varus for greater than 95% of the corresponding phase, and "Changer" otherwise. Patient characteristics of the Stable and Changer knees were compared to find associated factors. Results: Absolute variation of dHKA during gait was 10.9 +/- 5.3 degrees for the whole cohort. The variation was less for the varus knees (10.3 +/- 4.8 degrees), than for the valgus knees (12.8 +/- 6.1 degrees, p = 0.008). We found low to moderate correlations (r = 0.266 to 0.553, p < 0.001) between sHKA and dHKA values for varus knees and no significant correlation for valgus knees. Twenty two percent (36/165) of the knees were considered Changers. The proportion of knees that were Changers was 15% of the varus versus 39% of the valgus (p < 0.001). Significance: Lower limb radiographic measures of coronal alignment have limited value for predicting dynamic measures of alignment during gait.