ARTHRITIS OF THE HIP JOINT

METAL ON METAL HIP REPLACEMENT
VS
CERAMIC ON CERAMIC HIP REPLACEMENT

There are many hip implant designs available to the surgeon. There is no universal agreement as to which design is best. Each surgeon selects what he believes is best for the patient, or what he was trained to use, or in some cases, what his hospital forces him to use. Find out what implant your surgeon plans to use.

Each type of implant has unique surgical aspects and considerations which can only be learned by experience with many cases. Preferably, your surgeon should have had experience with hundreds of cases of the implant selected.

The basic design of the implant is similar regardless of brand.

The plastic socket (high-density polyethylene) is the hip implant’s weakest link. The plastic wears away at the rate of about one millimeter per year (about 1/40th of an inch), against a metal ball, giving the implant a life expectancy of 10 to 15 years.

Johnson & Johnson’s “Marathon.” polyethylene is one of several recently developed “cross-linked” polyethylenes that wear at a slower rate in the lab. It will take at least ten years of human usage before we will be sure that cross-linking is a true improvement.

Microscopic plastic particles are produced by daily wear, even with the cross-linked poly. They migrate between the implant and the bone. The body reacts to these “foreign particles” by producing enzymes which slowly dissolve bone. This may eventually result in loosening of the implant.

The metal parts of the implant are manufactured of Cobalt-chrome or Titanium. There is no agreement as to which is better. In some circumstances, each has advantages over the other. Cobalt-chrome has been used in the manufacture of orthopedic implants for 65 years, and is extremely well tolerated by the body. The AML stem is made of Cobalt-chrome. The socket is made of Titanium. In rare cases patients with metal allergies may have skin rashes, or chronic pain and swelling of the replaced joint which may be due to metal allergy. True rejection of the implant has never been reported. If you are allergic to any metals you need to let Dr. Huddleston know.

A huge breakthrough came with the 2002 introduction to the USA of metal-on-metal hips. Both ball and socket are made of Cobalt-chrome. It is believed that these will never wear out. Patients are allowed greater freedom of activity than with plastic sockets. There is some concern that the long-term frictional release of cobalt or chrome ions from the joint may be harmful to the human body. So far no deleterious effects have been reported in over sixteen years of use and careful study in Europe.

Note that in about 30% of patients, the metal parts of the hip replacement may trigger airport security devices. Use the plastic Joint Implant Card Dr. Huddleston’s staff will give you to show airport security.

An even newer development is ceramic-on-ceramic hips. The ball and socket are made of ceramic, which is not pottery, but the oxide of any metal, in this case, aluminum oxide. Wear is even less than with metal-on-metal surfaces, and there are no metallic ions to worry about. However, there is a 1 in 25,000 risk of the ceramic components fracturing. Re-operation may be required if either the ceramic ball or ceramic socket fractures. Setting aside the small risk of shattering, the all-ceramic hip is the best modern choice for all patients, but especially for the young and the active.

The all-metal and all-ceramic implants are expensive, and many hospitals and insurance plans refuse to pay for them, despite their long-term advantages. Dr. Huddleston recommends the metal-on-metal or ceramic-on-ceramic implants for all patients with fifteen or more years of life expectancy.

The hip implant parts are expensive, and there are many competing brands. Many hospitals contract with suppliers for a volume discount, and then restrict the surgeon’s choice to the contracted brand. That product may not be the best available, or the best implant for you.

Worse yet, some hospitals carry cheap, bottom-of-the-line, “low demand implants” for older patients, often defined as being over 65. The new metal-on-metal, and ceramic–on-ceramic designs are more expensive, and hospitals often restrict their use, even for younger patients.

You should find out if your surgeon is restricted in his choices by his hospital. If so, find a good surgeon who works out of a hospital that leaves the implant choice to him. Alternately, offer to pay the hospital the difference for the more expensive implant. The difference could be as little as $1000 before the hospital’s mark-up, and worth every penny.

Many older people these days are in good health, live very active lives, and expect to live well into their nineties. Clearly these are “high demand” patients who deserve a high quality hip replacement that will serve them well for the rest of their lives.

Choose the best surgeon, have him tell you exactly what implant he plans to install in your hip (brand name, manufacturer, and what the parts are made of), and then do some research to find out if it is what you want and need.

Dr. Huddleston’s hospitals do not restrict his selection of implants. He uses only the best implants available. He receives no royalties on implants. His choices and decisions are based solely on what is best for you.

A leg that is too short or too long is the most common reason for a lawsuit after hip replacement. A difference in leg length is more than an inconvenience requiring costly and unsightly shoe lifts. It can cause a limp, weakness of the hip muscles and chronic back pain.

The final length of the operated leg is determined by the level at which the “neck” of the femur is cut, the depth to which the socket is machined, and the size of the implants used.

Most surgeons try to make all these decisions before surgery, by measurements made on the hip x-rays. However, x-ray pictures are always magnified, by anywhere from 10% to 25%, compared to the real size of the bones. Most surgeons simply assume a magnification of 18% or so, as a “ball-park number”. In one study, the actual size of the implants was incorrectly predicted before surgery 60% of the time (six out of every ten patients!).

There are other sources of error. The anatomical landmarks for determining the level of the “neck” cut are not exact. The depth to which the socket is machined varies, depending on the shape of the socket, and the hardness of the bone.
Accurate leg length measurement is difficult, even with an uncovered patient, lying face upwards. But during surgery the patient is covered with layers of sterile drapes, and the operation is commonly done with the patient lying on the side. The “bottom leg” is bent at the hip and knee, is completely covered, and can not be measured easily for comparison. Finally, sometimes the surgeon will deliberately lengthen the leg a little for stability.

For all the above reasons, the leg length can be off by a quarter inch or more, and still be within an acceptable standard of care.

Dr. Huddleston uses a very accurate method for measuring leg length during the operation. His method has been published in orthopedic journals (refs). Other surgeons rarely use the method because it takes extra time and effort, or because they are unaware of it.

Patients return to normal walking much faster if they can put all their weight on the operated leg, starting the day after surgery. Most surgeons do not permit full weight for six weeks with un-cemented implants. This allows time for bone to grow into the implant until it is stable. However, if the fit is perfect, and the implant is totally stable at surgery, many surgeons allow full weight the next day.
If the implant is too large, the femur can fracture as it is driven down inside the bone, so the tendency is to under-size for safety. But, if the implant is very under-sized, the bone may fail to bond to it.

The correct implant size is therefore very important.

Most surgeons decide the size from hip x-rays taken before surgery, which is not very accurate, and make their final decision based on the “feel” of the instruments used to prepare the femur during surgery. In one study the size was incorrectly predicted from the x-rays 60% of the time (see “Leg Length” above).

There are twenty four stem sizes available with the Prodigy system, each slightly larger than the next. Dr. Huddleston makes his final selection based on an x-ray taken in surgery, with a metal sizing rod placed inside the femur. Very few surgeons do this. With such accurate sizing the implant fits perfectly every time, and more than 95% of Dr. Huddleston’s patients are allowed to bear full weight on the leg the day after surgery. However, if the bone is found to be very soft at surgery, and an un-cemented implant is nonetheless selected because of your age, weight bearing may be restricted for six weeks.

Dr. Huddleston takes an x-ray of the femur bone during surgery, with a sizing rod in place. This allows very accurate sizing of the non-cemented implant, and allows full weight on the operated leg, starting the day after surgery.

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On to the Next Section of the Manual:
Other Surgical Alternatives

 

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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.

Dr. H.D. Huddleston
The Hip and Knee Institute
5525 Etiwanda Ave., #324
Tarzana, CA 91356
Tel: 818.708.9090

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