In 20 anatomic specimens with an acetabular defect (type Paprosky 3b),
an acetabular component was implanted in the position of a high hip c
enter. The vertical migration of the hip center ranged between 13 and
35 mm. It was accompanied by a lateralization and ventral migration of
between 5 and 25 mm. The influence on the different abductor muscles
was calculated through computer model comparing muscle force and muscl
e length before and after implantation of a high hip center. The incre
ase in length of the gluteus maximus muscle and the posterior part of
the gluteus minimus muscle ranged between 1% and 6%, while all other e
valuated abductor muscles were shortened from 3% to 16%. The effect of
the simultaneous changes of the lever arms was an increase in necessa
ry muscle strength for pelvic stabilization from 140% to 250% compared
with the original estimated strength prior to implantation. This may
lead to insufficiency of the abductor muscles after placement of a hig
h hip center. On the basis of these findings, we do not recommend the
implantation of an acetabular component in the position of a high hip
center.