Accuracy of empirical distal femoral valgus cut angle of 4° to 6° in total knee arthroplasty: a randomized controlled trial

IntroductionCurrently, the best and simplest way that used to select the distal femoral valgus cut (DFVC) angle in total knee arthroplasty (TKA) is standing long leg radiograph. However, this kind of film is still not available in all hospitals. The purpose of this study is to compare the accuracy of different empirical DFVC angles in the restoration of the neutral mechanical alignment of the femoral component after TKA. Method125 patients who diagnosed primary osteoarthritic knee and underwent unilateral TKA were randomly assigned into three groups: A, B, and C, according to the use of an intramedullary guide with the DFVC angle of 4 degrees, 5 degrees, and 6 degrees, respectively. At three months after surgery, anteroposterior hip-to-ankle computed tomography (CT) scanograms were evaluated. Mechanical axis angle (MAA), mechanical lateral distal femoral angle (LDFA), femoral bowing, femoral neck-shaft angle (FNSA), and outliers of femoral component position were measured and compared among three groups. Independent influencing factors for the outliers >3 degrees were determined using binary logistic regression analysis. ResultsGroup B was older than group A. There were no significant differences of postoperative MAA, LDFA, femoral bowing, and FNSA among three groups. Outliers >+/- 3 degrees of femoral component position in each group were 14.6%, 19.0%, and 16.7%, respectively (p=0.865). When considering the outliers >+/- 2 degrees, group C (35.7%) had a trend to have fewer outliers than groups A and B (41.5 and 42.9%). However, this finding was not reached the statistical significance (p=0.778). Femoral bowing was only significantly influencing factors that related to the outliers >+/- 3 degrees (p=0.003). Conclusion This study demonstrates that there are no significant differences in coronal femoral component alignment among using the DFVC angle of 4 degrees, 5 degrees, and 6 degrees. The use of the DFVC angle of 6 degrees had a trend to reduce the outliers. Nevertheless, femoral bowing is the crucial influencing factor for selecting the degree of DFVC angle.