[Preventing malrotation during intramedullary nailing of femoral fractures].

Background: The problem of preventing malrotation after closed intramedullary nailing of femoral shaft fractures has not been solved yet. As clinical tests and radiologic criteria for intraoperative use provide little accuracy, the theoretical basis for a C-arm-based measurement of the femoral antetorsion was analysed.

Methods: The directions of femoral neck axis and condylar axis can be identified by the radiologic views "knee joint, lateral view" and "hip joint, axial view". The rotation of the C-arm in relation to a horizontal axis to achieve these views can be measured in degrees. Theoretically, the difference between these rotation angles could be used to calculate the antetorsion. Intact plastic femora (Sawbone) and a femoral shaft fracture model were used to research optical and geometrical phenomena that influence a direct measuring technique.

Results: Several geometrical phenomena were observed, making direct measurement with arithmetic corrective factors not recommendable. For practical reasons, a data table was created, correlating the difference between the two C-arm angles with true antetorsion. In an interobserver trial with 18 trauma surgeons, the method proved to achieve high accuracy with a maximum interobserver variation of 5 degrees.

Conclusions: The method is easily reproducible, reliable and can be recommended to every surgeon. Due to the wide range of physiological antetorsion angles in different individuals, fair results can be expected controlling the rotation with standard value tables, and excellent results can be expected using bilateral measurement.