Hip Implants
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Volume III, Issue 2
Summer 1992

Selecting a Hip Implant: Whether or Not to Use Cement
By Dr. Thomas P. Gross
The indication or reason to perform a hip replacement is usually for relief of the pain that occurs when a hip joint is destroyed. Dr. Murzic explained this matter in more detail previously (Joint Effort, Summer 1991). After it has been decided that a patient is a good candidate for total hip replacement, the next major question to resolve is what type of implant to choose. There are many different brands available, all with slightly different features which are claimed to give their prosthesis an advantage; few of these claims have been proven. However, implants can be placed into two broad categories according to the way they are fixed to the bone. Some are cemented to the bone with polymethylmethacrylate (PMMA), while others rely on bone to grow into grooves or pores on the surface of the prosthesis to provide fixation (uncemented). There continues to be a great deal of controversy among orthopedic surgeons about when to use each of these types of hip implants.

To better understand the issues involved it may be useful to first review the history of hip replacement surgery. In the mid 1800s surgeons simply removed the bone around joints and left the limb to flail. Later various tissues such as muscle or skin and even materials such as nylon and glass were placed in the space left by the removed bone in order to create an artificial joint. In 1939 Smith- Peterson developed a fairly successful technique of cup arthroplasty, where the femoral head is smoothed off and then a metal cup is simply placed over it without being fixed to either bone. In the 1940s the Austin-Moore prosthesis was developed. A large metallic ball was used to replace the femoral head and it was fixed to the femur using a metal stem that was “press fit” into the femoral canal. Later, the McKee-Farhar implant provided a metallic cup, which was screwed into the acetabulum as well as a ball and stem to allow both sides of the joint to be replaced. A major breakthrough occurred in 1960 when Charnley introduced his low friction arthroplasty. For the first time both the femoral and acetabular implants were rigidly fixed to the bone using dental cement (PMMA) and motion occurred between metal and plastic (ultra high molecular weight polyethylene, (UHMWPE) surfaces. This resulted in a dramatic relief of pain and resulted in the wide spread use of total hip replacements.

Early results were encouraging but by 10-15 years in “high risk” patients (younger, overweight or more active) the cement was noted to crack and loosen in a high percentage of patients. When the cement bond breaks down, the implant becomes loose resulting in bone destruction and pain. In order to provide a longer lasting interface or attachment of the implant to the bone, two approaches have been taken. Some surgeons have concentrated on improving cement techniques. Current methods include thorough cleansing of the femoral canal using a water jet, plugging the canal, retrograde injection of cement using a cement gun, pressurizing the cement before inserting the prosthesis, and using cement spacers to centralize the prosthesis. With these improvements only 1-2% of components loosen after 5 years.

Long-term results are not yet available. Other investigators began developing implants with bone in-growth surfaces for use without cement. The surface of the implant is coated with a layer of beads or wire mesh of the appropriate size (porous coating) to allow the bone to grow into it. The first of these implants to be widely used was in fact a slight modification of the Austin-Moore implant with a porous coating applied, the AML implant. Many other variations have followed. Without cement, the major cause of loosening seen in the past is eliminated. Theoretically the implant could remain fixed indefinitely. The implants for the acetabular side have worked so well that cement is now rarely used to fix this component. Several problems have been recognized with the femoral implants during their initial use. First, some fail to become attached with bone. Sometimes the fibrous (scar) tissue holds the implant well enough that there is no or minimal pain. In others the pain is worse and the implant needs to be exchanged (reversed). Since there is no cement ‘grout’ to fill in the gaps between the implant and the strong cortical bone, in uncemented replacements, it is very critical to use an implant that fits well. Our approach has been to use a custom designed implant to achieve the best possible fit. Second, in some implants the porous coating has detached from the stem often resulting in failure of the implant. To avoid this we have begun using grooves machined directly into the implant, and coated with bone mineral (hydroxylapatite).

Dr. Taylor has discussed this development in a previous issue (Joint Effort, Summer 1990). The mineral increases the rate of bone ingrowth into the grooves and there is no porous layer that can fail. Third, between 5 and 20% of patients receiving uncemented femoral implants develop some pain in the thigh. Usually this is mild and related to being overly active after receiving their hip implant. Rarely is the pain as bad as before surgery. The exact cause is still unknown. In our experience using a custom implant, 6% of patients have mild thigh pain. Fourth, acetabular plastic liners were made thinner with the first uncemented implants resulting in increased wear debris in the joint and some actual breakages of the liner. The wear debris may actually result in destruction of bone around the implants and result in loosening. Currently we are using acetabular components that have been completely redesigned to allow a maximum amount of polyethylene thickness to be used. Finally, there is a concern about stress related bone loss. It occurs around all implants, including cemented ones, to some degree but appears to be most pronounced with thick uncemented implants with extensive coating. It occurs around the top of the femur and could potentially weaken the bone to the point that revision would be extremely difficult if it becomes necessary. The custom implant has a coating only on the top third of the implant to minimize this potential problem.

Cemented implants have the advantage of providing immediate fixation, allowing them to take weight immediately. There is, at most, a 1-2% rate of thigh pain. They are significantly cheaper. With current cement techniques they appear to be much more durable than once believed. From earlier studies, there are still serious concerns that the cement bond is not durable enough in younger, heavier, more active persons. Also, if revision becomes necessary, there is usually much more bone loss when a cemented component loosens. A patients’ longevity must also be considered. Currently the life expectancy of women is 77 years and it is slightly less for men. On the other hand, in patients who have reached the age of 60-65, their life expectancy is greater. If a person has serious medical conditions such as diabetes, heart disease, kidney failure or cancer, one must try to estimate how this would decrease their life span. Obviously only a very approximate estimate can be made. It would be ideal if an implant could always be selected to last the patient the rest of his/her life.

With all these factors in mind, we must formulate some recommendations regarding the use of cemented vs. uncemented implants. As previously mentioned, the results with uncemented acetabular implants have largely been abandoned. Because cemented femoral components with modern cement techniques are proven and probably reliable for at least 10 years, we recommend these in patients who are age 65 and older, lighter than 200 pounds, and not excessively active. Despite the good initial short-term results, we do not have available long-term data to be sure that they will outlast cemented implants, although on theoretical grounds we believe that they will. In patients who are younger than 65, are over 200 pounds, or are extremely active, it probably is worthwhile to accept the additional problems and risks of a newer less proven technique that has the potential for a better long term result.

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Annual Golf Tourney
The 1992 Pete Dexter UnGolf Tournament will be held on Friday, August 14, at Haggin Oaks Golf Course.

It will be a 7:30 a.m. shotgun start and the $100 per person fee benefits Friends of Orthopaedic Research. A barbecue and awards banquet will be held at 1:30 p.m.

Checks should be made payable to Sacramento Regional Foundation and mailed to The Sacramento Bee, Community Relations Department, P.). Box 15779, Sacramento, CA 95825.
For more information, call (916) 321-1800.

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Staff Profile: Jane Bislend, RN
I was born in a small town in Southwestern Oklahoma called Sentinel, the 10th and last child of a cotton gin manager and his wife of many years.

After an uneventful childhood, I went into nurses training (Wesley Hospital in Oklahoma City) at the beginning of WWII and became one of the first members of the Cadet Nurses Corp. This was a government sponsored program requesting that we spend our last six months of nurses training in a government hospital. I chose an amputee center in Temple, Texas at Ford Hood.

My husband and I came to California in 1952. I did office nursing for four years then on to Sutter General Hospital in 1960 doing all types of nursing from recovery room, intensive care, emergency room, IV therapy, to general floor duty. I took the position of head nurse on the orthopaedic floor from 1970-1978.

During this period I had two children, a boy and a girl, who as adults have made me very proud.

I came to work for Dr. Bangar and Dr. Taylor four years ago to relieve Inez, the editor, while she was ill and somehow I’m still here.

I can say I particularly love this job as most of our patients are in my age group and we can identify with many things. Dr. Taylor and I work well together. He is smarter but I am older.
My favorite hobbies are reading adventure novels, traveling and baking for the staff.

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From the Editor’s Desk
As many of you know, Mary Minix, Certified Medical Assistant & Extremities Radiological Technician has been on maternity leave since the end of May. On June 1st she and her husband became the proud parents of an 8 pound, 10 ounce baby boy – welcome Jaden. I have been filling in as her temporary replacement.

In April I worked a day in the office to refresh myself with the procedures, mostly paperwork. I saw several long-standing patients I knew, some from my university days. It really was uplifting to be active in the office again. Since Mary is back she will return to x-ray and Betty to nursing.
- Inez Willett

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Introducing The New Fellow
Born and educated in Texas, Ronald E. Talbert, M.D. will join Dr. Bargar in August as his new fellow for a year of specialized training in joint replacement. Dr. Talbert received his medical training at the University of Texas-Galveston, and completed his internship and orthopaedic residency at the University of Texas, San Antonio. He is presently finishing a tour of duty with the U.S. Air Force in Nevada and will be relocating to the Elk Grove area with his wife, daughter and son.

Dr. Talbert will be replacing Dr. Gross who, at the completion of his fellowship with Dr. Bargar plans to go into private practice at Fresno Orthopedic Associates, with emphasis on joint reconstruction. Our best wishes for a successful future to Dr. Gross.

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International Award
Dr. William Bargar and Dr. Howard Paul recently accepted the Computerworld Smithsonian International Award for Information Technology in the Arts and Sciences for Medicine on behalf of Integrated Surgical Systems (ISS). ROBODOC is the computerized surgical system, which uses advanced imaging software and a robotic arm to prepare bone for hip replacement surgery.

ISS was one of only two California organizations to win a Computerworld Smithsonian award this year, and only the seventh from the state in the award’s four year history. The theme of this year’s awards was “The Search for New Heroes.”

As many of you are well aware, ROBODOC is under review by the Food and Drug Administration for use in human total hip replacements and the first surgery should approval be granted by the FDA will be performed by Dr. Bargar at Sutter General Hospital this year.

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