The required resultant abductor force and the available resultant abductor force after operative changes in hip geometry.

The required abductor force (Freq) and the available abductor force (Fav) are calculated for different positions of the hip rotation center (RC) and different greater trochanter (GT) shifts in the frontal plane of the body in the one-legged stance. It is biomechanically favorable that Fav exceeds Freq and that the magnitude of the resultant hip joint force (R) after the operation is decreased. The difference between Fav and Freq, which represents the relative abductor strength, increases after medialization of RC and after lateralization of GT. On the contrary, after medialization of GT and after lateralization of RC, the difference decreases, which has unfavorable biomechanical effects. Distalization of GT is favorable because it increases the relative abductor strength.