Femoral pulse as a guide to the mechanical axis in total knee arthroplasty.

The anatomic relationship of the center of the femoral head to the femoral artery was studied in 140 hips in 70 patients. The coronal plane distance between the femoral artery 2.5 cm below the inguinal ligament and the center of the femoral head was measured on pelvic arteriograms. The femoral artery was found an average of 7.7 +/- 5 mm medial (range, -3-22 mm) to the center of the femoral head. The femoral artery was within 15 mm of the center of the femoral head in 93% of cases reviewed. A 76-cm theoretical mechanical axis was used in estimating clinical angular changes in the axis for a given coronal plane difference. By use of this model, the range of variability translates into a maximum change in the mechanical axis of 1.66 degrees and up to only 1.2 degrees in 95% of the cases reviewed. A marker placed just lateral to the palpable femoral pulse approximately 2 to 3 cm below the inguinal ligament is suitable as a guide to locate the center of the femoral head when determining the mechanical axis during total knee arthroplasty.