Variances in sagittal femoral shaft bowing in patients undergoing TKA.

We asked, "What are the quantitative variances in sagittal femoral bowing in patients who were indicated for total knee arthroplasty?" We retrospectively evaluated 145 consecutive patients who underwent 166 primary total knee arthroplasties with adequate preoperative nonrotated sagittal plane full-leg lateral radiographs. Digital radiographs were processed such that each femoral shaft was divided into three segments. A purpose-written program determined the flexion/extension of the femoral component using the Knee Society method of focusing on the distal femur and a second method using the whole femur. The median angle of curvature of the proximal, middle, and distal thirds of the femora were 5.4 degrees, 0.2 degree, and 3.1 degrees, respectively, with the largest bow occurring in the proximal segment followed by the distal segment and with the least bow in the middle segment. The median angles for femoral component flexion were considerably different with the whole femur angle showing more flexion (4 degrees) than that of the Knee Society angle (1.421 degrees). We found an inverse relationship between distal angle of curvature and height as well as weight. Men had greater proximal bowing and less distal bowing than women. The effects of these variances may have implications in development of osteoarthritis and total knee arthroplasty component survival.