CT determination of femoral torsion.

Femoral torsion has been measured in infants and children by computed tomography. The method requires two scans, one through the femoral neck, another through the femoral condyles. A specially designed device and packing about the knees assures immobilization of the legs. Slight variations in the positions of the sections in the neck and condyles do not alter the measurement significantly. Intraobserver and interobserver errors are low, 2 degrees and 3 degrees mean error, respectively. The radiation required involves small tissue volumes at about 1.7 R (4.4 x 10(-4) C/kg). Measurements are more difficult when the femoral necks are short or vertically oriented. The method appears to have sufficient accuracy for clinical purposes.