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What are the differences between the
posterior and anterior surgical approaches?
Recovery is quicker with the posterior approach because no
important muscle groups are sectioned. The posterior
approach is also well-suited for patients who are large,
well muscled or who require special techniques to implant
the hip resurfacing socket.
To improve stability and reduce the incidence of dislocation
after THR, some surgeons changed from the posterior to the
anterior approach. Even a hip resurfacing procedure
technically can be performed in most individuals using an
anterior approach but this requires removal of 33% to 50% of
the abductor muscles. Even though the muscle group is
reattached, the muscles are strong and, therefore, the
reattachment may pull loose even if activities are
restricted for a prolonged period. Further, the data that
indicates improved stability in THR with the anterior
approach involved patients in whom the ball size utilized
was very small (ie., between 22mm and 28mm). It is now
possible, due to the newer, more wear resistant bearing
technology, to use much larger balls and, hence, there is no
advantage with the anterior approach. Wear data now
available supports the use of larger ball sizes from 36 mm
up to 54mm with Metal on Metal technology and up to 40 mm
with new cross-linked polyethylene. The largest ball size
available for ceramic on ceramic bearings is 36 mm because a
two part socket is required and ceramic material must be
relatively thick to minimize the risk of fracture.
Summary of Advantages - Posterior vs. Anterior Approach:
The posterior approach for hip resurfacing has the following
advantages now that the instrumentation has been redesigned
specifically for that approach:
1. No important muscle groups are sectioned. 2. There is no
release of the abductor muscles. They are the most important
muscles stabilizing the hip during walking and other
activities. 3. The gluteus medius and minimus remain intact.
The only muscle groups that are released are the short
rotators that are repaired at the conclusion of the
procedure. However, no important gait or other disturbances
results from a release even if they are not repaired because
the rotation is accomplished by other muscles. One of the
two insertions of the gluteus maximus tendon which extends
the hip may be released and if so then repaired. The other
insertion remains intact and there has been no significant
physiological damage to date. 4. The new instrumentation
facilitates a smaller incision especially in thin
individuals. A longer incision is necessary in well muscled
or overweight patients. A slightly longer incision is
necessary in resurfacing than when the head and neck are
amputated in conventional THR. In hip resurfacing the
surgeon must work around the head and neck to be able to
prepare the acetabulum and implant the socket accurately.
Hip resurfacing is technically more demanding and takes
slightly longer. Since hip resurfacing is an anatomical
replacement, leg length equalization is facilitated and more
precise. Leg length equalization in THR is more demanding,
less certain and requires an intra-operative X-ray. 5. The
anterior approach requires removal of some of the abductor
muscles for either hip resurfacing or THR. Even though they
are repaired this reattachment may not be 100% successful.
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