There are no significant difference in coronal femoral component alignment among using distal femoral valgus cut angle of 4 to 6 degrees, the resection with valgus angle of 6 degrees has the trend to reduce the outliers.
Currently, the best and simplest way that used to select distal femoral valgus cut angle in total knee arthroplasty (TKA) is long standing AP hip to ankle radiograph. However, this kind of film is still not available in all hospitals. The purpose of this study is aimed to compare the accuracy of different empirical distal femoral cut angle in the restoration of the mechanical alignment after TKA.
126 patients who diagnosed osteoarthritic knee and underwent unilateral TKA were recruited and randomly assigned into 3 group: A, B and C according to the use of intramedullary guide with the distal femoral valgus cut angle of 4 to 6 degrees, respectively. CT scanograms of whole leg were taken at 3 months after surgery. Femorotibial angle (FTA), lateral distal femoral angle (LDFA), femoral neck shaft angle (FNSA), coronal femoral bowing (CFB) and outliers of femoral component position were recorded and compared among three group. Risk factors for outliers were determined using logistic regression analysis.
There are no significant differences in postoperative FTA, LDFA, FNSA and CFB among three groups. Outliers of 3? in each group were 15.0, 19.0 and 16.7%, respectively (p = 0.886). While outliers of 2 degrees were 42.5, 42.9 and 35.7%, respectively (p = 0.755). Excessive CFB (>5 degrees) is the only one significant risk factor for outliers (p = 0.005).
Although there are no significant difference in coronal femoral component alignment among using distal femoral valgus cut angle of 4 to 6 degrees, the resection with valgus angle of 6 degrees has the trend to reduce the outliers. In this study, CFB is the important influencing factor for selecting the degree of distal femoral cut.