Radiologic determination of rotation deformity of the femur - Computed tomography, optimized measurement accuracy and radiation exposure

58 Patients, suspicious to have rotation deformity of the femur, were examined. To compare the Value of diagnostic methods in measuring the degree of malrotation we estimated this degree using clinical examination and calculated the anteversion of the femoral neck, taking radiographs in the technique of Dunn and Rippstein, and a modified method of computed tomoghraphy. Only in twelve cases the direction of malrotation was corresponding in all three methods, although considerable variations in quantitative results were noted. Maintaining the exact position of the patient, necessary to get reproducible results using conventional X-ray technique, was impossible in most cases of patients with posttraumatic joint-stiffness and malalignement. Determination of femoral neck anteversion using this modified method of CT is a quick, reproducible technique to calculate the degree of malrotation, insensitive to the position of the patient. By means of this CT method it was possible to approach the highest accuracy in precise preoperative planing. Furthermore the radiation exposure could be reduced in a range of 20%-40%.