HIP REPLACEMENT

The modern Hip Replacement 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 replacements have been performed in the U.S. since then.

The operation has become fairly routine and is successful around 98% of the time.

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 long-term problems with hip replacements are wearing out of the socket, and loosening of the bond between the implant and the bone. In time the cement can crack, directly resulting in loosening. Secondly, the body reacts to minute fragments of cement and plastic, 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 have recently been in the news.

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 so far been excellent, especially in people with good bone quality.

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.

On the other hand, uncemented socket components have been extremely successful, regardless of the patient’s age. Cement is rarely used on sockets nowadays.

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), from midway between front and side (antero-lateral approach), or through a two incision approach (one anterior, and one posterior).
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.

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.

The mini-incision hip replacement is an important recent development. It is used with the posterior approach. In the past the skin incision was ten or more inches long. With special new instruments, this approach is now possible through an incision as small as three inches in thin patients. In obese patients, the incision is less than half what it would otherwise have been.

A smaller incision means less blood-loss. There is also less trauma to the muscles and ligaments around the hip, so much less pain, and an even quicker return to normal walking. Few orthopedic surgeons have learned the posterior mini-incision. Fewer still can do a perfect hip replacement, with accurate leg length, through such a small incision. Dr. Huddleston routinely uses the mini-incision posterior approach, or the two incision approach (see below).

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.

IN THE ANTERIOR APPROACH the whole operation is done through a single incision in the groin. The muscles are not cut, but are spread apart. The ligaments that hold the hip together still have to be cut. The procedure is done under x-rays. The operation is risky, even in the best hands. It is very difficult to line up the femur bone through this incision, and see it clearly. There is much room for error in the placement and sizing of the femoral component, as well as in getting the leg length right.

THE TWO-INCISION APPROACH is a very recent development. Two 3-inch incisions are made: one in the groin, as in the anterior approach, and one over the back of the hip. Muscles are not cut, but are spread apart, and are disturbed less than with any other approach. Normal walking returns sooner with this approach than with any other, sometimes in as little as two weeks. The operation is difficult, and very few surgeons have been trained to do it. Dr. Huddleston has taken special cadaver training in the use of this approach.

Dr. Huddleston performs the operation using a posterior approach with a mini-incision, or the two-incision approach. With either approach there is much less pain, less blood loss, and normal walking returns sooner.

 

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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