Short knee radiographs can be inadequate for estimating TKA alignment in knees with bowing

ABSTRACT

Purpose@#The aim of this study was to compare the discrepancy of alignment categorization in total knee arthroplasty (TKA) between the anatomical femorotibial angle (aFTA) measured on short knee radiographs and the mechanical hip– knee–ankle axis angle (mHKA) measured on full-length radiographs in knees with and without bowing. @*Methods@#From January 2014 to June 2017, 107 of 526 osteoarthritic knees at our hospital were found to have femoral or tibial bowing. Bowing was defined as a femoral bowing angle (FBA) > 3° or 2° or 7° , mHKA> 3°) alignments. We compared the categorization of alignments between knees with and without bowing using the McNemar test and used logistic regression to find factors for the alignment discordance. @*Results@#Coronal alignment was discordant in 26.2% of the knees with bowing and 13.1% of the knees without bowing (p < 0.001). FBAs were a significant factor affecting the discordance of alignment categorization (OR = 1.152, 95%CI 1.038– 1.279, p = 0.008). @*Conclusion@#Short knee radiographs are insufficient for estimating coronal alignment after TKA, particularly in knees with femoral bowing.Level of evidence: III: Retrospective comparative study.