Hip Replacements Can Loosen

Osteolysis viewed as #1 cause for revision

For people suffering with intense pain and limited mobility
from hips damaged by arthritis, hip replacement surgery
can seem like a miracle.  Although it is miraculous, hip
replacement is not always a permanent solution.

People who have their first hip replacement when they are
in their sixties or older are likely to live the rest of their
lives without needing revision of their hip replacement.

However, younger patients are more likely to need revision
surgery at some point. Wear of the materials and loosening
of the implant are the most common reasons for needing
revision surgery.

Hip implants are designed to replicate the ball and socket
structure of the normal hip in human anatomy. The hip implant
consists of a component which fits into the pelvic socket or
acetabulum, commonly a metal cup with a plastic polyethylene
lining, and a metal ball on a long stem which fits into the
thigh bone or femur.

As normal wear occurs, the friction caused by the metal ball
rubbing against the polyethylene plastic lining can result
in the degradation of the polyethylene and the flaking off
of the small polyethylene particles.

The body's immune system reacts to the particles as foreign
matter and attacks it. Since the particles typically settle
near the implant, the immune system also attacks surrounding
bone, a process known as osteolysis. As bone loss occurs,
the hip implant can loosen and begin to function improperly.

Osteolysis is regarded by many orthopedic surgeons as the
number one cause of hip implant failure. Other causes include
incomplete fixation and infection. When implant failure
occurs patients must have another surgery to replace the
failed implant, known as revision hip replacement surgery.

Since valuable bone can be lost when an implant fails,
revision surgery is more complicated than the primary or
original hip replacement.

Though the procedure for revision hip replacement is similar
to primary joint replacement, there are some differences:

   Revision surgery takes longer than the primary surgery
   because it is more complicated.

   Joint aspiration may be necessary to ensure no infection.

   Revision surgery requires more blood than the primary
   surgery.

   Since revision patients are typically older, a more
   extensive pre-op examination may be needed.

   The risk of complication and recovery period are greater
   for revision surgery.

   Revision surgery often necessitates the replacement of
   lost bone either by bone grafting or the use of special
   implants.

   Revision implants may be cemented or uncemented but the
   design of the implant may differ from the original implant.

Since revision surgery is regarded as more difficult, it is
imperative to have an experienced surgeon and seasoned
surgical team. A properly equipped hospital ready for any
situation is a consideration as well. New implants such as
metal-on-metal and ceramic-on-ceramic are being tried now
with the hope that they will prove to be more durable. It
still will take one or two decades before that durability
can be truly assessed.

REFERENCE:
Arthritis of the Hip & Knee, Ronald J. Allen, Victoria Anne
        Brander, M.D.,  S. David Stulberg, M.D.
About Total Hip Replacement, Sulzer Orthopedics