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.