This is also a frequent problem though not as common as one of loosening of
the socket. 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 femoral component to sink downwards in the femur bone
due to the loosening. The rough outer surface of the cement layer attached to
the component tends to have a sandpaper effect on the bone causing wearing away
of the inner side of the femur bone. The damage to the bone allows the sinkage
and also the tilting of the femoral 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 femoral 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 implant that does not
rely on bone support in the area of the bone loss, a longer implant that will
achieve fixation in previously unused bone and bypass the area of the weakness,
a modular femoral component that allows the use of "build ups" to
compensate for the bone loss and recreate the length of the bone, a femoral
component with supplemental screw fixation across the shaft of the femur bone
and the use of solid structural bone graft material.
Whether the failure has resulted in a fracture of the bone in the femur:
This can sometimes occur when the problem of femoral component loosening
has been left unattended for a substantial period of time. If there is a crack
fracture through only one side of the femur bone, then this can be dealt with
by the use of some bone graft at the time of a fairly standard revision of the
femur.
On the other hand, if the fracture extends right across the bone in a transverse
or oblique direction causing the lower part of the femur to become discontinous
from the upper part, then a supplemental plate fixation with bone grafting is
neccessary. Purpose designed plates and cables are available for the purpose.
The state of the acetabular component and whether that would need also to
be redone:
In carrying out his preoperative planning the surgeon would want to check the
acetabular component to see if that needed redoing. At times, it is only during
the surgery that direct visual inspection of the bearing surface would reveal
whether or not it needed to be replaced.
Is there a fracture of the implant:
Fortunately, this has become less frequent nowadays with the advances in metallurgy
in the last 15 years or so. However, one still comes across patients with the
older implant (and occasionally a modern one) where it has fractured within
the femur bone. It is important to plan for this problem as removal of the far
component particularly if it is well fixed, can be difficult and may require
the bone to be opened or "windowed". Also, the new implant would need
to cross the area of any weakness from opening or windowing the femur so as
to reduce the risk of fracture postoperatively. This is becasue thee windowed
area acts as an area of weakness and the normal stresses and strains on the
femur can cause a break or fracture if the area is not protected during the
healing process.
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