- Need a new hip? Someday you may grow your own.
- 'Fix-me itis' fueling boom in joint surgeries
- Risk Assessment Tool for Osteoarthritis
- Wall Street Journal: Pushing Limits of New Knees
- New York Times: Getting a New Knee or Hip? Do It Right the First Time
- Dr. Bal in the News...
TestimonialsDr. Bal's Patients Tell Their Stories
"I am very satisfied with the outcome of my surgery and the improved quality of life I am now enjoying..."
Shamsy Kazemi-Bardool, Iran
"I am looking forward to being able to boat and golf this summer, without having to endure the pain and limitations of prior years..."
Greg Voreis, Mo.
"Just 9 ½ weeks following my surgery knee replacements, I traveled to Hawaii and went scuba diving..."
David Booker, Mo.
"Dr. Bal did great a job explaining the procedure through conversation and with his hip surgery book. He changed my life..."
Dennis Disselhoff, Mo.
"It is so important to have a physician who you trust, and who will listen to you. That's critical. I have never seen a doctor who cares so much for each and every patient..."
Faye Bleigh, Mo.
"I am glad to have come to Dr. Bal; his office staff was great to work with; the hospital experience was very good, and the outcome of surgery was all I had hoped for..."
Craig Jacobson, Ne.
"I feel so free now. Last weekend I rode my bike to Cooper's Landing and enjoyed a great meal as I watched the Missouri River roll by and listened to the bluegrass music..."
Marilyn McCreary, Mo.
"The staff at Capitol Region were very gracious, attentive and thorough. I would go back there anytime. They made sure I was comfortable..."
Bob Smith, Mo.
"It has been a real pleasure to meet and get to know Dr. Bal. He is caring, thorough in his explanations, and a great friend...."
Richard Wallace, Mo.
6. Artificial Hip Components
Information for Hip Patients
1. Anatomy of the Hip
2. Arthritis of the Hip
3. Treatment Options
4. Surgery Options
5. Hip Replacement Surgery Basics
6. Artificial Hip Components
7. Preparing for Hip Replacement Surgery
8. Recovery from Hip Replacement Surgery
9. Managing Pain or Discomfort
10. Life with an Artificial Hip
Exercise Guide for Hip Patients
(click to download PDF)
How do the implants work in a hip replacement?
You have a natural socket called the acetabulum in the pelvis bone. The hip ball normally sits in this socket. By reaming away the damaged bone and cartilage, fresh bone is exposed, and a slightly oversized hemispherical socket made of a sturdy, inert titanium alloy is impacted into your bony socket. Usually this impaction does not require fixation with screws since the mechanical press-fit is snug enough. Into this titanium shell, a bearing surface of polyethylene, ceramic, or metal is then locked mechanically.
Next, the femur (thighbone) is prepared by cutting off the arthritic femoral head (the ball of your hip joint). The cavity inside the femur bone is enlarged, and a slightly oversized femoral implant is securely impacted into the femur. The stem has a metal junction at its top end, designed to fit an artificial ball. This ball is made of a cobalt-chrome alloy, or ceramic, and matches the diameter of the bearing earlier fitted inside the artificial socket.
Once the ball is placed in the socket during surgery, the surgeon must adjust leg lengths, implant stability, muscle tension, and range of movement of the hip joint. This is where surgeon judgment and expertise are critical. The new artificial ball will rotate inside the synthetic shell just like a natural hip ball and socket would, except the artificial parts will not produce any pain.
What materials are used in a hip replacement or resurfacing?
The structural parts are made of titanium alloy; structural means that the skeleton grows and bonds permanently to these parts. Alloy means that the metal is not pure titanium. It is a mixture of other metals, to enhance the safety, performance, and avoid possible allergic reaction to any one metal.
Titanium alloys are used for this purpose because of durability, biocompatibility, several decades of experience, and the fact that titanium is less stiff than other metals and therefore better suited for skeletal reconstruction.
The bearings are mounted on the structural parts, using specially engineered tapers. Bearing surfaces in the hip are made of plastic, metal, or ceramic. The choice of bearing depends on the individual patient.
In engineering hip replacement components, the structural parts are optimized for their ability to bind to living bone and for long-term biocompatibility and durability, while the bearings are optimized for the lowest wear rates.
What do you do on the socket side of a hip replacement?
On the socket side, or the pelvic side of a hip replacement or resurfacing, a metal half-shell is fitted inside the patient’s own bony socket. Inside this shell, a locking mechanism fastens the bearing, which can be polyethylene, metal, or ceramic.
What do you do on the femur side of a hip replacement?
On the femur, or thighbone side, the inside cavity of the thighbone is enlarged, and a metal femoral stem is implanted in this cavity, where it will bind to the bone. On this stem, an artificial ball is attached using an engineering taper. The ball is made of either cobalt-chrome metal, or ceramic.
What brand of hip implants do you use?
We typically use Zimmer brand of implants. The Zimmer metal socket is a model called the “Continuum Cup” and the femoral stem is called the “M/L taper.” These designs have withstood the test of time, with excellent long-term results. Implant companies make several models and designs of implants, and the precise application depends on individual patient needs and anatomy.
The most common bearing surface that we use in hip replacements is a cobalt-chrome ball with a cross-linked polyethylene socket liner. This bearing is built upon decades of experience with standard (non cross-linked) polyethylene; the material offers more flexibility and options to make hip replacement safe and predictable.
If you have a strong preference for a certain type of joint prosthesis, or a certain type of material, we can discuss using that implant and material.
There is very little difference between the implants offered by the major manufacturers. No implant company pays us to promote or use any product.
What if I want a different brand of hip replacement?
Simply let us know. Because of our emphasis on research and investigation, we embrace the latest technology, biomaterials, and surgical methods.
Be cautious about the unregulated marketing and promotion of hip and knee implants though. Orthopaedic companies and hospitals want business, and their advertisements rarely give the complete picture. We can offer unbiased opinion about different implants, while respecting whatever decision you make in this regard.
How much do the parts used in hip replacement weigh?
The parts weigh about 3 to 5 pounds. The bone removed during hip replacement weighs a little less. So, you may gain a few pounds of body weight as a result of hip replacement surgery. This is more than balanced by the fact that people tend to lose weight after surgery from diminished appetite, and the stress of an operation.
Why does an artificial hip wear?
Everything wears out over time. Artificial hip bearings are no exception. During everyday activity, our hips endure several million cycles a year. People who are athletic or walk more than usual will load their joints even more. Cyclic loading leads to wear, even though modern hip bearings are extremely wear-resistant. But, no bearing surface is completely wear-proof.
Realistically, for most patients, bearing wear in an artificial hip is not a practical concern. Assuming the surgery is done properly, most modern hip bearings will last longer than the patient’s lifespan.
Where do wear particles from the artificial hip go?
All hip bearings produce microscopic wear particles that collect in the soft tissue envelope around the artificial hip. This layer of tissue, called the hip capsule, forms around the prosthetic joint after surgery. Cells in this layer act like a “biological sink” by absorbing and storing the wear particles.
Some wear particles migrate into the body, and are spread by the circulating blood to remote organs, such as the heart, liver, spleen, lymph nodes, etc. No study has shown any adverse impact of such wear particles from artificial hips that are spread throughout the body, although this remains an area of investigation and research.
What is the advantage of ceramic bearings in hip replacement?
Ceramics are synthetic materials, used in industrial applications. When used in orthopaedic bearings, their wear rates are extremely low.
This is an area of research interest for us; we completed an FDA-approved trial of ceramic hips some years ago. Those bearings are now available for use by community surgeons in the United States.
A disadvantage of ceramic bearings is that there are fewer options for the surgeon. This is related to engineering limitations. With future developments, ceramic bearing use may become more widespread. Today, for most patients, a cobalt-chrome ball and cross-linked polyethylene offers the best trade-offs between safety, longevity, flexibility, long-term wear, and sizing options.
Can ceramic parts be used in my hip replacement?
Yes. We can use a ceramic ball and a plastic socket. Or we can use ceramics in both the ball and the socket. Either combination offers extreme wear resistance and durability.
Old design ceramics were brittle, and the extreme hardness of ceramic materials limited their use in hip replacement. The newer ceramics are super tough alloys, especially engineered for the orthopaedic market. They are safer, and have excellent long-term outcomes, with almost zero wear.
Even newer ceramic materials made of silicon nitride are in development; we expect to conduct a clinical trial of silicon nitride bearings, pending FDA approval. Silicon nitride offers even less wear, with extreme durability and strength.
When do you use cement to fix the hip components?
Cementing implants is reserved for the elderly, and for cases in which the bone anatomy requires a cemented implant. The majority of hip replacements are done without bone cement.
In decades past, cement was used extensively to attach metal parts to bone. We now rarely use cement in hip replacements because of developments in biomaterials and implant design.
How durable are cemented parts in hip replacement or resurfacing?
Data from hip replacements done many decades ago show that cemented total hip sockets usually loosened up after 10 to 15 years and that cemented femoral stems usually loosened up after 15 to 20 years. Today, cement is rarely used in hip replacements; in fact, if a previously cemented hip replacement has come loose, the parts used in repeat surgery are of a cementless design. Such components are designed to heal to native bone; this type of skeletal fixation has almost indefinite durability.
How do cementless hip implants attach to bone?
They attach by healing directly to bone. Metal surfaces are designed with a porous honeycomb metal structure, into which bone can grow. This biologic fixation is very strong and will not loosen over time.
While bone is growing into such parts, initial stability relies on a mechanical fit between metal and bone. This is achieved by physically impacting or hammering the parts into bone during surgery.
Can I get the same hip implant that a famous celebrity has?
Implant companies use celebrities to promote hip replacement, typically showing the youthful lifestyle, and active involvement in skiing, golf, and other outdoor activities. Please view all marketing and promotional information with skepticism; such information is not always complete.
In reality, participation in sports such as golf and other activities is just as possible with one brand of hip components as the other. No brand in the market today is superior in terms of returning patients to activities faster, or in giving patients an advantage in a specific sport, no matter which celebrity a company pays to tout its products.
Do I need a custom implant or instruments made from CT/MRI studies?
Hip components come in many sizes, configurations, models, and geometries. Off-shelf components give a precise fit in nearly all the patients. In some cases involving congenital abnormality, special-sized components can be ordered if necessary.
Custom-built implants based on CT scans or MRI scans are unnecessary, and to date, have no proven benefit other than marketing value for the manufacturer, hospital, and surgeon, as well as a higher cost for the patient and the health-care system.
Do you use human tissue or parts for hip replacement?
In routine total hip replacement, no such tissue is needed. Many years ago, we used allograft bone in some complicated cases to restore deficient bone. But with newer metal composites that can be shaped like bone, human tissue is no longer necessary for hip surgery.
In fact, metal augmentation techniques have advanced such that we can help patients who in the past were probably beyond help. The ability to rebuild hips that have had multiple operations previously, and restore people to function is a practical advantage of innovation and improvement in our health-care system.
Can patients develop an allergy to the artificial hip?
Such occurrences are exceedingly rare. Most commonly, what is often called an allergy is a missed, subtle infection. True metal allergies are usually well known to the patient ahead of time. In such unusual cases, it is possible to use components made of alternative metals, based on allergy testing, to which the patient is not sensitive.
At the time of this writing, there is some concern that metal-on-metal bearings (the use of a cobalt-chrome ball with a matched cobalt-chrome socket bearing) may cause an allergic reaction in some patients. If there are further developments in this area of knowledge, we will update this information on our website.
Hip replacement components
Hip resurfacing components
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