if opposite hip is normal, it may be used as a template;
normal hip center should be restored when possible (this will reduce joint reactive forces);
generally the the component is placed as far medially and as far inferiorly as possible;
management of superior displacement of hip center
the amount of superior displacement is defined relative to the inter-tear drop line;
minor superior displacement is represented by 1-2 cm of displacement whereas 3-4 is more significant;
high hip center placement:
this is the time proven method and has the least number of technical pitfalls;
indicated for an oblong cavity (which does not allow creation of a hemisphere without disruption of anterior or posterior column)
allows for contact between the host bone and the acetabular component making it possible for bone to grow into a cup that has been inserted without cement (allows the component to be in contact with living host bone);
is preferable to the use of a structural graft under some conditions
as Harris (1998) points out, a high hip center is not a biomechanical disadvantage as long as there has not been component lateralization;
technique requirements:
sufficient bone stock for cylindrical reaming;
hip center is not lateralized (ie bone stock will allow for medialization);
acetabulum is shaped into a hemisphere, with the apex made more proximal than the lateral edge of the acetabulum;
smaller appropriate sized component placed into the superior portion of the recess;
note that quadrant system may not be safe with the high hip center placement;
limb length must be correctable with use of a long-neck or calcar-replacement femoral component.
low placement of the hip center:
technique options:
insertion of cement to fill the deficient superior roof essentially eliminates the possibility of subsidence (which is seen in allografts) and has a survivorship of 92% at 10 years (Ash SA, et al, (1996));
