This is one of the commonest problems faced by revison hip surgeons. Most commonly,
the sockets being revised are the ones that have been implanted with cement.
In evaluating an individual patient's case, the surgeon will want to assess
The current position of the implant:
It is not unusual for the socket component to move upwards in the pelvis due
to the loosening. The rough outer surface of the cement layer attached to the
socket tends to have a sandpaper effect on the bone causing wearing away of
the upper part of the socket. The damage to the bone allows the shifting of
the socket implant. The patient may notice shortening of the leg.
The amount of associated bone loss:
Small to moderate amounts of bone loss, partcularly when contained within the
confines of good bone, do not appear to have a detrimental effect on fixation
of the new acetabular component. The surgeon may choose to use some partculate
bone graft.
If there is more signficant bone loss, then the surgeon will have to use a technique
that compensates for this. The options are the use of an acetabular reinforcement
shell with supplemental screw fixation, an acetabular reinforcement shell with
an inferior hook and screw fixation, an anti-protrusio cage and massive solid
structural bone graft material.
Whether the failure has resulted in a fracture of the bone in the socket:
This can sometimes occur when the problem of socket loosening has been left
unattended for a substantial period of time. If there is a fracture through
the floor of the socket but the bone of the rim remains intact, then this can
be dealt with by the use of some bone graft at the time of a fairly standard
revision of the socket.
On the other hand, if the fracture extends right across the acetabulum in a
transverse direction causing the lower part of the pelvic bone to become discontinous
from the upper part, then a supplemental plate fixation with bone grafting is
neccessary.
A marginal fracture or one affecting a small sector of the acetabulum does not
require to be separately addressed.
The state of the femoral component and whether that would need also to be
redone:
In carrying out his preoperative planning the surgeon would want to check the
femoral component to see if that needed redoing. If that was the case, then
he or she would remove this implant as a part of his approach to the socket.
This tends to make the operation of revision of the acetabulum easier.
If the femoral component was not loose, then the next consideration would be
to note whether it was cemented and if so, whether it could be easily removed
and reinserted without damage, as part of the exposure of the socket.
If the implant had been inserted without cement in the first place and if bone
had ingrown onto it, then its removal would not likely be wise or safe. In that
case the surgeon may choose an alternative plan to access the acetabular component.
The size of the femoral ball and whether that is modular (removable without
taking out the whole component):
The surgeon would want to note the type of the femoral ball and its size.
If the femoral ball was modular, then it would be possible to detach it from
the femoral component at surgery and replace it at the end.
On the other had, if the ball was not modular and the implant was not to be
removed, then he would have to ensure that he had sockets available to him during
surgery that matched the size of the femoral ball. While this is not usually
a problem, on the odd occasion, there may not be sockets available of the right
size to "mate" with an old style femoral ball.
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