Preoperative Hip to Ankle Radiographs in Total Knee Arthroplasty

Whether a preoperative long leg radiograph taken with the patient standing helps the surgeon reproduce a normal mechanical axis after total knee arthroplasty is unknown. The purpose of the current study was to evaluate whether a preoperative long leg radiograph helps to restore normal limb alignment after total knee arthroplasty. Ninety-four patients (124 primary total knee arthroplasties) were randomized to either receive or not receive a preoperative long leg standing radiograph. Patients with previous hip or ankle surgery, femoral or tibial fracture, deformity of 15° or greater, or those who were obese (body weight index > 40 kg/m²) were excluded. All arthroplasties were done by one surgeon. The angle of distal femoral resection varied between 5° and 8° (mean, 6.2°) among patients with long leg radiographs. In patients without long leg radiographs, the distal femur was cut at 5°. Long leg radiographs were obtained postoperatively in all patients and the mechanical axis was assessed, first by whether the mechanical axis fell within the central third of the knee, and second by the distance in millimeters that the mechanical axis fell from the knee center. No significant difference in the postoperative mechanical axis was detected between the two groups. Eighty-six percent of the patients with long leg preoperative radiographs and 92% of the patients without long leg preoperative radiographs had the mechanical axis pass through the central ⅓ of the knee. Preoperative hip to ankle long leg radiographs taken with the patient standing did not significantly help to obtain a neutral mechanical axis during routine total knee arthroplasty.