The axes of long bones are very useful in defining how the mechanical (weight, gait, flexion, extension, etc) forces impact the morphology of the bone structure. They help in the surgical planning of deformed bones.
Video summary[edit | edit source]
Mechanical axis of long bones[edit | edit source]
The mechanical axis of a long bone is a straight line connecting the joint center points of the proximal and distal joint regions, whether in the frontal or sagittal plane (Fig. 3a).
Anatomical axis of long bones[edit | edit source]
The anatomic axis of a bone is the mid-diaphyseal line (Fig. 3b). The anatomic axis line may be straight in the frontal plane but curved in the sagittal plane, as in the femur.
Distance of mechanical and anatomical axes[edit | edit source]
In the tibia, the frontal plane mechanical and anatomic axes are parallel and only a few millimeters apart. Therefore, the tibial anatomic-mechanical angle (AMA) is 0° (Fig. 3c).
In the femur, the mechanical and anatomic axes are different and converge distally. The normal femoral AMA is 7±2° (Fig. 3c)