The efficacy of intramedullary femoral alignment in total knee replacement

The angle formed between the femoral anatomic axis and the femoral prosthesis was measured on radiographs of 201 total knee arthroplasties. The radiographs were taken on a 51 inch x 14 inch cassette and had to have satisfactory centering and minimal rotation to be included. All total knee arthroplasties had intramedullary femoral alignment. The mean femoral component angle (relative to the femoral anatomic axis) was 6.1 degrees valgus, with a standard deviation of 2 degrees and a range from 2 degrees to 12 degrees valgus. Seventeen knees (8.5%) had a femoral component angle that was < or = 2 degrees valgus or > or = 10 degrees valgus. In 4 knees, medial femoral bowing of the distal third of the femoral shaft caused an excessive valgus cut. In 7 knees, a capacious femoral canal was present that potentially allowed for divergence of the relatively undersized guide rod in the canal. Overall, 8.5% of cuts were believed to be less than ideal. Preoperative radiographs of the entire femur should identify patients in whom errors are more likely and allow for templating the amount of distal femoral bone to be resected. Extra caution is needed in bowed femora and in capacious femoral canals.