[Computed tomographic torsion-angle and length measurement of the lower extremity. The methods, normal values and...

Complex corrective osteotomies in the lower extremities require precise preoperative planning. Fifty patients (37 male, 13 female) with an average age of 31 years (13 to 61 years) who had suffered fractures of the lower limbs and had been treated by osteosynthetic or conservative methods were studied, using a GE 9800 Quick CT; accurate and reproducible measurements of the angles of torsion of the femur and tibia were obtained. Digital images were produced to standardise the planes of measurement and to measure the length of the limb. The normal extremities of patients older than 18 years showed internal torsion of -20.4 +/- 9 degrees of the femur and external torsion of 33.1 +/- 8 degrees of the tibia. The most important clinical measurement is the intra-individual difference of the torsional angles. Amongst normals this is 4.3 +/- 2.3 degrees in the femur and 6.1 +/- 4.5 degrees in the tibia. Consequently, only angles greater than 9 degrees in the femur and 15 degrees in the tibia should be regarded as abnormal. Radiation exposure was measured by a LiF-thermoluminescence dosimeter on an Alderson phantom. Skin dose was 6.3 +/- 1.2 mGy and gonadal dose for females was 2.5 +/- 0.3 mGy and for males 0.7 +/- 0.1 mGy.