Radiological analysis of normal axial alignment of femur and tibia in view of total knee arthroplasty.

Alignment of the anatomical and mechanical axes of the lower extremities was analyzed using standardized radiographs in two series of 66 femur and 44 tibia specimens. A new anatomical axis, the distal femoral anatomical axis, was introduced. This axis corresponds to the overall femoral anatomical axis and encloses a valgus angle of 6 degrees with the mechanical axis of the femur. It allows for design of shorter intramedullary guiding instruments that will still be in congruency with true femur geometry. Comparison with computerized calculations of angles on computed tomography scans on a series of 38 bones shows a high precision of measurement on standard radiographs in neutral rotation.