Does Use of a Variable Distal Femur Resection Angle Improve Radiographic Alignment in Primary Total Knee Arthroplasty?

Background The distal femur resection in total knee arthroplasty (TKA) is commonly made using a fixed angle relative to an intramedullary rod. This study's purpose was to assess if a variable distal femur resection angle technique improves femoral component alignment in TKA. Methods This was a review of primary TKAs performed by 2 surgeons. One surgeon used a fixed resection angle of 5° for varus and 3° for valgus knees (“fixed” cohort). The second used hip-knee-ankle (HKA) radiographs to measure the angle between the femoral anatomic axis and a line perpendicular to the femoral mechanical axis, which was used as the resection angle for each patient (“variable” cohort). Femoral component and HKA alignment were measured from standing HKA radiographs by 2, independent, blinded observers. Two hundred ninety patients were needed for power to detect a 15% difference in femoral component “outliers” (target of 0° ± 2°; significance = P < .05). Results Three hundred twenty consecutive patients were included with no differences in age, body mass index, or preoperative deformity (P = .3-.8). A 5° resection angle was used in 46.3% of the variable and 80.0% of the fixed cohort patients. A total of 80.2% of femoral components in the variable and 63.1% in the fixed cohort were within 0° ± 2° (P = .002; 84.6% of variable and 56.3% of fixed for valgus knees, P < .001). The mean HKA alignment was improved in the variable cohort (−1.4° ± 3.3° vs −2.6° ± 3.3°, P = .001). Conclusion Use of a variable distal femur resection angle improves femoral component alignment after TKA.