[A criterion of validity of the x-ray computed tomographic measurement of femoral neck anteversion].

A wrong patient's position on the CT scan table may lead to mistakes in the measurement of femoral neck anteversion. We present an experimental demonstration using a wood manufactured femur model. If the slices are performed with flexion of the thigh, the measurement is lower than the true value. Thus, to check the measurement on the picture of added slices, it is necessary to have a superimposition of the pictures of the upper part and the lower part of the femur. Otherwise, the measure is wrong and the mistake depends of the direction of the shifting: --if the lower part of the femur is higher, the anteversion measure is lower than expected. --if the lower part of the femur is lower, the anteversion measure is higher.