Stemmed Total Hip Replacement

Stemmed total hip replacement is by far the most commonly used. John Charnley was the first to make this a routinely successful operation in the 1960’s. Numerous modifications have occurred since his time. Several millimeters of bone is removed from inside the socket and a metal implant with a porous ingrowth surface is tightly implanted into the prepared bone bed. A bearing liner is then locked into place in the implanted metal shell. This leaves a much smaller cavity for the ball.

Therefore the head and neck of the femur must be amputated. A stem is then fixed into the hollowed marrow canal of the top of the femoral shaft using either cement or bone ingrowth technique. A smaller (than natural) ball is then attached to the trunion of the stem (morse cone taper junction). This ball fits into the smaller socket liner.

Hip Surface Replacement

Hip surface replacement accomplishes the same basic goal as sTHR with much less bone removal and preservation of normal biomechanics. Bearing size and femoral offsets remain the same as for the normal femur. This was tried in the 1950’s by Charnley with Teflon implants, by others with primitive metal on metal bearings, and in the 70’s with metal on plastic bearings. Finally Derek McMinn applied modern metal on metal bearings to resurfacing in the 1990’s. Mainly because the femoral head is preserved, it is much more difficult for the surgeon to get adequate access to accurately place the deeper socket component.

In stemmed THR, the head and neck are amputated early in the operation allowing much easier access to the deeply placed socket. This technical difficulty the primary reason why many hip surgeons are reluctant to perform this operation. It has been demonstrated in numerous scientific papers that the complication rate is much higher when surgeons are learning this operation. This learning curve extends for several hundred cases. Difficulty in placing the socket component accurately is one of the major contributing factors to recent problems with adverse wear failure.

Hemi-Surface Replacement for Osteonecrosis

One option to minimize wear debris and tissue reaction is to eliminate the artificial bearing by replacing only the diseased part of the joint. A hemi-surface replacement was sometimes recommended in the past for patients who had osteonecrosis of the femoral head (also referred to as avascular necrosis) and had intact remaining articular cartilage on the acetabulum or pelvic side.

The hemi-surface replacement preserves and maintains bone by providing physiological stress transfer to the femoral neck and proximal femur. It avoids inflammatory reaction and loosening due to any artificial bearing wear debris. However, if only one half of the joint is replaced, the degree of pain relief is not as good as if both sides of the joint are replaced. It is not always possible to convert this to a total hip resurfacing. I do not advise the use of this operation.