The resultant bending moment Mbend , acts in the middle of the femoral neck and perpendicular to the neck axis, and is calculated with the following formula:
The forces (Fx’, Fy’, Fz’) and moments (Mx’, My’, Mz’) are measured in the “implant coordinate system” x’, y’, z’ centered in the middle of the implant head. The force component Fx’ acts laterally, Fy’ anteriorly, and –Fz’ distally along the femur axis. The measured moment components Mx’, My’, and Mz’ turn right around the x’, y’, and z’ axes. N is the distance between the head center and the middle of the femoral neck and is equal to ½ L.
Mtne acts around the neck axis of the femur and represents the torsional loading of the neck. It is calculated by α = -45° rotation of the “bone coordinate system” around the y-axis.