HIP REPLACEMENT

The modern Hip Replacement (also known as Hip Arthroplasty) was invented in 1962 by Sir John Charnley, an orthopedic surgeon working in a small country hospital in England. His work has been one of the great triumphs of Twentieth Century surgery.

The arthritic femoral head (i.e., the femoral head) is removed, and replaced with a metal ball. The ball has a metal stem which is anchored into the hollow space inside the femur bone with bone cement. The worn out socket is replaced with a plastic socket. The painful parts of the arthritic hip are thereby completely replaced with metal and plastic surfaces. The plastic socket has a very low frictional resistance, and a very low wear rate against the metal ball. Hip replacement was first performed in the United States around 1969.

Many hundreds of thousands of hip replacements have been performed in the U.S. since then. Hip surgery has become safe and is extremely successful.

The operation has become fairly routine and the chances that you will be completely happy with the outcome is about 98%

One of the first three American surgeons to perform this type of surgery was Charles O. Bechtol. He started a total hip replacement program in 1969 while he was professor of orthopedic surgery at UCLA. Dr. Huddleston studied hip and knee surgery with him for one year as his assistant. The two later because partners in a private practice restricted to total joint replacement. Dr. Bechtol retired in 1984 and Dr. Huddleston took over the practice, and merged the practice with the Southern California Orthopedic Institute in 1988.

The major problems with standard hip replacements are: wearing out of plastic sockets, loosening of the bond between the implant and bone (either cemented or un-cemented). In time the cement can crack, directly resulting in loosening.

Secondly, the body reacts to minute fragments of cement, plastic or metal, and attempts to remove them, but unfortunately the process also removes bone adjacent to the particles, leaving the bone structurally weakened. If the implant loosens, a second surgery may become necessary to reattach it. There has been much research into the loosening problem. It was widely believed that the solution was to eliminate the cement. This led to the development of the:

Cementless Hip Replacement in which the surface of the metal parts is porous, and looks like coral. Bone can grow into the metal pores and bond the implant to the bone without the use of cement. There are many manufacturers and many brands of hip replacement implants. Some designs have had a very poor track record. Fortunately Dr. Huddleston has never used the Sulzer hip implants which had a high rate of failure, or Zimmer’s Durom Socket which has also recently been in the news because of a high rate of failure.

The AML Total Hip Replacement (manufactured by DePuy/Johnson & Johnson) is the most widely used cementless implant in the world, and has the longest track record (since 1978). Dr. Huddleston uses the improved AML hip replacement known as the Prodigy. The long-term results with the AML hip have been excellent. No other hip implant in the world has been shown to have better longevity.

Initially, the cementless hips were used in patients of all ages, but it was soon found that in people with soft bones (osteoporosis), the femur bone does not always bond to the porous metal. Cement is still used with very soft bones, regardless of age. Bone quality can usually be determined from the hip x-ray, but, quite frequently a true assessment of bone quality can only be made at surgery. Dr. Huddleston’s final decision on the question of cement will be made in your best interest. Currently Dr. Huddleston cements less than 5% of the hip replacement he performs.

On the other hand, uncemented socket components have been extremely successful, regardless of the patient’s age. Cement is rarely used on sockets nowadays, and about 95% of the stems are inserted without cement.

Major recent developments have been the introduction about eight years ago, of cross-linked polyethylene for manufacture of plastic sockets, and the introduction of metal-on-metal hip replacements, in which both the ball and socket are made of metal.  Both developments greatly increase the lifespan of a hip replacement, but both have their own potential problems. Plastic sockets are mainly used in older patients with shorter life expectancy.

Surface Replacement came into vogue in the 1980’s. It had a metal cap and a plastic socket. It was off the American market within four years because of the high failure rate of this combination. Dr. McMinn, in Birmingham, successfully re-designed it ten years ago, with a metal socket against a metal cap. The FDA cleared the Birmingham Surface Replacement for use in America in 2006. It is highly recommended for younger patients. Dr. Huddleston is an expert on Surface Replacement.

The most recent important new developments have been minimally invasive hip replacement, and pain management for hip replacement.

Bone grafts are occasionally needed to restore bone defects. If so, the bone may be obtained from the discarded femoral head, or from the pelvis, through a small separate incision. Occasionally it may be necessary to cut tendons in the groin (“Adductor Tenotomy”) if these tendons restrict hip motion. This is done through one or two separate half-inch incisions in the groin, and does not result in loss of function.

It is possible to perform two hip replacements under the same anesthetic, and Dr. Huddleston does do it in selected cases, but generally does not recommend it, since it greatly increases the risk of complications. If you need two hips replaced, a better course is to have the more painful hip replaced first, and to wait 12 weeks or more before undergoing the second operation.

The hip joint can be approached from the front of the hip (anterior approach), from the back (posterior approach), from the side (trans-trochanteric approach), or from midway between front and side (antero-lateral approach).
With the side-approach the trochanter bone is cut, and later re-attached with steel wires. This was the standard for many years, but is now only occasionally used for re-operations.

In ANTERIOR HIP REPLACEMENT the operation is performed through a single incision in the groin. This approach is between muscles, and not a single muscle or tendon is cut. The incision is usually about four inches long and is minimally invasive. This is the most painless approach, with the shortest time to full recovery, including driving, and including normal walking without a cane or other support. It has the lowest risk of dislocation, and there are no restrictions after the surgery as there are with the other approaches. The incision is usually about four inches long. It is a more difficult and risky approach, and the surgeon needs special training. Not every patient is a good candidate for Anterior Hip Replacement.

THE GLUTEAL SPLIT is a significant improvement of the posterior approach. The gluteus maximus muscle arises on the pelvis and attaches to a broad flat ligament, the Facia Lata, which in turn attaches to bone at the knee.

In a standard posterior approach about two and a half inches of the gluteal muscle fibers are split to the junction with the Facia Lata, which is incised for a further four inches in the same line (see illustration), for a total of six to eight inches.

It turns out that not cutting into the Fascia Lata hugely facilitates a rapid return to normal walking.

However, splitting the muscle without cutting the fascia gives a very small window through which to do the surgery. Safe surgery through this two and a half inch incision has only recently been made possible by the development of special instruments.  One small tendon, the pyriformis, is cut and reattached at the end of the operation. This tendon has been routinely cut in hip surgery for over a hundred years, and cutting and reattaching it is in no way detrimental.

This Gluteal Split hugely shortens the time to normal walking. Most patients can walk with a single cane within two days of surgery and are off the cane after about a week. The key is staying out of the Fascia Lata.

THE POSTERIOR APPROACH is the one used by most surgeons. Small, unimportant tendons (short rotators) are detached to get to the hip joint, and re-attached later in the operation. Normal walking returns much sooner than with the antero-lateral approach, sometimes in less than six weeks. Ninety percent or more of all hip surgeons use this approach. Although the recovery is slower than with the Anterior Approach or the Gluteal Split, there is nothing wrong with this approach, and the end result after six months will be just as good, as long as the surgeon did a good job to begin with.

Minimally Invasive Hip Replacement (mini-incision hip replacement) is an important recent development. It is used with the Gluteal Split and the Anterior Hip Replacement approaches. In the past the incision was routinely ten or more inches long. With specially designed new instruments, the operation is now possible through an incision as small as two and a half inches in a thin patient, and in obese patients the incision is less than half what it would otherwise have been. However, it is not the length of the skin incision that is important. It is what goes on under the skin that counts.

With minimally invasive hip replacement there is less trauma to the muscles and ligaments around the hip, so, less blood loss and less pain, and a much quicker return to normal walking. Few orthopedic surgeons have mastered the posterior mini-incision (Gluteal Split) and fewer still the Anterior Hip Replacement. Very few can do a perfect hip replacement, with accurate leg-length, through such a small incision. Dr. Huddleston routinely uses the mini-incision Gluteal Split, and Anterior Hip Replacement approaches.

THE ANTERO-LATERAL APPROACH, is the second most commonly used. The chance of hip dislocation is thought to be less with this approach. However, there is a trade-off. About one third of the most important hip muscle (gluteus medius) is detached from the bone, and later re-attached. This weakens it, leaving most patients with a limp, sometimes for up to a year.

The surgeons of the Hip and Knee Institute perform hip replacement surgery using the anterior  Approach, or the Gluteal Split.

 

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Arthritis of the Hip Joint copyright © 2005 Herbert D. Huddleston, MD.
Arthritis of the Knee Joint copyright © 2005 Herbert D. Huddleston, M.D.

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