Hip Resurfacing - Frequently Asked Questions
What is hip resurfacing?
The hip is a ball-and-socket joint. The "ball” is the head of the femur, or thigh bone. The “socket” is the cup-shaped form of the acetabulum, or pelvic bone. The surfaces of the hip joint — the head of the femur and the acetabulum — get worn and deformed with arthritis and other degenerative conditions, causing hip pain. An arthritic hip and what it looks like after resurfacing are shown in the figure below. Hip resurfacing is an operation that resurfaces (rather than replaces) the worn ball. The socket part of the operation is the same as a total hip replacement.
Figure 1. Worn out ball-and-socket of hip joint shown at left , with arthritis and destruction of the joint space. To the right is shown a resurfacing. The joint is resurfaced with metal.
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Is it really a new procedure?
No. Hip resurfacing was originally done 30 to 40 years ago, but failed because of poor materials and design. Since then, the materials and design have been improved. The current version of hip resurfacing is the third generation of this procedure.
The Birmingham Hip Resurfacing System is made by a company called Smith & Nephew Orthopaedics , and it is among several designs scheduled for release in the U.S. market. Some advance marketing of this procedure has already made it to several news sources. Patients should be cautious in interpreting claims of a “new” procedure and should understand the surgery and its limitations thoroughly. The figure below will show you a photo of a Birmingham hip resurfacing.
Outside the United States , hip resurfacing implants are more readily available. In the United States , the most recent version of hip resurfacing has been in clinical use since 1997 , with more than 60 ,000 implantations worldwide. At this time , the Smith & Nephew implants are the only ones approved by the U.S. Food & Drug Administration (FDA) for use by orthopaedic surgeons , although many other manufacturers will release similar implants for this procedure shortly.
Figure 2. The worn-out ball of an arthritic hip joint is shaped with instruments to accept a metal cap made of high carbide cobalt-chrome. This cap is precisely matched to the polished inside surface of the metal socket which is also shown above. The metal socket has a roughened surface on the outside to help it grow into the pelvis bone. The metal cap has a short tail above for alignment during surgery. In all models of hip resurfacing today, the cap is attached with bone cement, while the socket is attached without bone cement.
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How is “hip resurfacing” different from a “total hip replacement”?
On the socket side, nothing is different in terms of the surgical procedure. Uncemented metal sockets have had excellent clinical outcomes in the last 20 years and reflect the modern standard. In both hip resurfacing and replacement, the degenerative socket is prepared by special metal reamers driven by a power device. Into this hemispherical cavity, a metal socket is impacted in, and sometimes screws are used to attach it to pelvic bone. These days, screws are often not necessary, because the metal socket is slightly oversized compared to the bony socket. The metal sockets come in various diameters to fit the patient’s anatomy and size.
One difference in socket preparation is subtle and makes no difference in recovery. But it should be mentioned for the sake of full information. In total hip replacement, the metal socket, once placed in the pelvis, is usually capable of accepting various bearing inserts. In other words, the surgeon has the choice of various bearing surfaces, such as polyethylene, ceramic, or highly-polished metal to line the inside of the socket with. These bearing inserts click into the metal shell, which is first installed in the patient’s pelvis.
In contrast, with hip resurfacing, the only bearing surface available is metal on the socket side. When this happens -- when metal is used on the socket side -- the surgeon must use metal on the ball side also. This means that the actual bearing coupling is metal-on-metal. While this is durable and well-proven, there is a theoretical concern about the accumulation of small metal particles with long-term wear of the joint. This applies to any metal-on-metal bearing, whether in a hip replacement or a hip resurfacing.
On the femur side (thigh bone), the preparation of a hip resurfacing is quite different from a hip replacement. With hip replacement, the ball is cut off and removed, and the inside of the femur bone is reamed up to a desired size. Then, a metal spike called a femoral stem is driven into the femur bone, usually designed to grow into the bone, although bone cement can also be used. At the top end of this metal femoral stem, a ball is attached to a special taper. The femoral stem is usually made of a very strong metal alloy, typically cobalt-chrome-molybdenum. The surgeon has control of the neck lengths built into the ball, so that leg lengths can be adjusted.
A hip resurfacing does not cut away any part of the top end of the thigh bone. The patient keeps the original hip ball, it is simply ground down and capped, or “resurfaced” as hip resurfacing implies. This is an advantage of the procedure, in that bone is preserved. For many patients, the reliability, predictability, and outstanding long-term results of a total hip replacement will be the better and more durable option. For a small group of patients who are young and in whom a repeat surgery is anticipated in the future, the hip resurfacing is a better option since the preserved bone makes the second, future operation easier and more durable.
With modern minimally invasive techniques applied to hip replacement, and to hip resurfacing, hip stability and leg lengths can be controlled by the surgeon. We specify no hip precautions with either procedure since the surgery is now less invasive, and muscles are preserved. If any change in leg length is desired however, only hip replacement can achieve it. With hip resurfacing, the leg lengths cannot be altered from what they are before surgery.
The figure below shows a hip resurfacing and a hip replacement on the AP (front to back) x-ray view.
Figure 3. The x-ray to the left shows a hip resurfacing done on the right hip of a patient. This view is taken from front to back. The x-ray on the right shows a hip replacement, also on the right hip of a different patient. The only practical difference between the implants is in the preservation of bone with the hip resurfacing.
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Can a minimally invasive surgical approach be used with hip resurfacing?
Yes, a minimally invasive hip resurfacing procedure has been developed. The minimally invasive procedure typically uses an incision of 4-5 inches in length compared to the standard approach, which requires an incision of 10-12 inches in length. The minimally invasive procedure allows for less soft tissue damage and a quicker recovery. It is important to realize, however, that not all surgeons trained to perform hip resurfacing procedures can also perform the minimally invasive technique.
Our minimally invasive procedure for hip resurfacing is based on a variation of the MIS-2-incision total hip replacement. Essentially, the front incision of this operation is used to do a hip resurfacing, with no muscle cutting, and a much easier patient recovery. The second incision is not necessary. The procedure is not for every surgeon, nor hospital. It requires special equipment and training. In our practice, the equipment is available and our surgeons have the special training and experience in minimally invasive surgery that can be applied to hip resurfacing.
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What is the bearing surface in hip resurfacing?
The only bearing surface, or the point of contact between the ball and socket implants, is metal-on-metal, in the hip resurfacing procedure available today. Both bearing surfaces (ball and socket) are highly polished chrome cobalt alloys that are closely matched in diameter. This metal has a long history of use in orthopaedic procedures such as hip and knee replacements.
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What lubricates a hip resurfacing?
The lubricant is called synovial fluid. This lubricates a hip replacement or any other artificial joint in the human body. Synovial fluid is a thick, greasy liquid that is produced by cells that line the joint cavities. It reduces friction in the joint, just like grease in an automobile suspension joint. Synovial fluid enters the space between the implant’s ball and socket joint to help lubricate its movement as you move your hip.
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Is there a choice in the bearing surface in hip resurfacing?
The bearing surface used in hip resurfacing today is limited to metal-on-metal. The metal used is highly polished high carbide cobalt chrome. You should review the (theoretical) risks related to metal-on-metal bearings, described below.
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What are the risks specific to hip resurfacing?
Please read this carefully, since many promotional and marketing efforts may neglect to discuss this critical information.
Because the hip resurfacing procedure uses a metal-on-metal bearing surface, an increase of metal ions in the blood and urine may occur. There is currently no evidence that metal ions from this procedure produce any health problems. Still, to be safe, it is recommended that those who are pregnant, or plan to become pregnant, or have decreased kidney function should not have metal-on-metal implants.
So far, all the evidence shows that metal-on-metal bearings are safe, and data from overseas going back several decades seem to support this safety.
A unique risk of hip resurfacing is that the preserved bone under the ball may break, or that the femoral ball which is capped with metal may collapse. These complications usually occur within a year or two of surgery, and if they occur, the treatment is a second operation, i.e., conversion to a total hip replacement. To revise a failed hip resurfacing to a total hip means that a femoral stem must be inserted in the femur. The socket does not have to be changed. Also, because bone is preserved with a hip resurfacing, the hip replacement does not entail any more bone loss than if you had chosen a hip replacement in the first place.
Finally, with our improved minimally invasive surgical procedures, it is now possible to do both the hip resurfacing, and if it should fail, the conversion to a hip replacement through the same, minimally invasive surgical technique.
The standard risks and complications related to any surgery still apply to a hip resurfacing, and you should review this information elsewhere on this web site.
In summary, the risk of early loosening of the cap covering the ball of the femur is something you need to be aware of if you choose a hip resurfacing procedure. Fortunately, this occurs rarely. And when it does occur, the salvage is to convert the hip resurfacing to a hip replacement, i.e., the operation you would have had if you had not chosen the hip resurfacing. Exposure to metal ions is a theoretical concern at this time, but if you are worried, you should avoid a hip resurfacing.
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Who should consider hip resurfacing?
Patients suffering from hip pain due to degenerative joint diseases like osteoarthritis, rheumatoid arthritis, traumatic arthritis, dysplasia or avascular necrosis. When this pain is no longer manageable by the usual means, such as pain medication or physical therapy, or if hip function decreases enough to interfere with daily activities, the hip may need to be surgically repaired. Hip resurfacing is intended for patients either of a younger age or higher level of activity, as these patients are more likely to require a future hip joint revision. Since the procedure saves more of the patient’s natural bone, future hip joint surgery is relatively simple.
Most patients who are candidates for hip resurfacing are under 55 years of age, but the surgery is still an option for individuals older than 55 as long as they are physically active, do not have a severely deformed hip joint, and have adequate bone density. X-rays, examination, and a patient history can usually help decide who can benefit from this operation.
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Are there long-term data showing that hip resurfacing can last?
Since hip resurfacing was reintroduced in its current form in 1997, patient results have been at least as good as conventional hip replacement. However, this is still too recent to know what the procedure’s long-term results may be. Available statistics show us that five years after hip resurfacing, more than 90 percent of patients still have the implanted device in place, without revision; report good results on objective scores; and are either “pleased” or “extremely pleased” with the results of their surgery.
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Are there any restrictions after hip resurfacing?
No, and particularly not if done with a minimally invasive surgery approach. The recovery time for hip resurfacing is shorter than for any standard hip replacement, and when combined with minimally invasive hip surgery, the results are better in terms of pales pain, quicker recovery, no precautions, and returning to usual activities. Return to full activity can be expected to take around 2-4 weeks on average. Your hip will have improved range of motion and strength.
Some precautions do apply to hip resurfacing though, and these are designed to avoid the small risk (around 1 percent) of a femoral neck fracture, i.e., the neck part of the thigh bone breaking off. High-impact activities such as running and jumping should be avoided for several months after hip resurfacing. After that, there are no restrictions beyond listening to what feels right to your body.
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Who should not consider hip resurfacing?
Due to specific health risks, some patients should not consider hip resurfacing. Elderly patients or those leading sedentary lifestyles are generally not recommended for this procedure. Patients who are pregnant or may become pregnant, or who have weak bones, kidney trouble, metal allergy/sensitivity, rheumatoid arthritis that is poorly controlled or that requires prednisone treatment, insulin dependent diabetes, lupus or other immuno-compromising diseases such as amyloidosis are not good candidates for hip resurfacing.
The indications and contraindications for any implant surgical procedure are complex and require the input of an experienced surgeon. Please discuss these issues with your surgeon. In general, hip resurfacing is contraindicated if any of the following apply to you:
- You have an infection of the body or blood;
- Your bones are not yet fully grown;
- You have any blood vessel-related diseases, muscle-related disease, or nerve-and-muscle-related disease that will prevent the implants from remaining stable or that may prevent you from following directions during the recovery period;
- Your bones are not strong enough or healthy enough because of severe bone loss (osteoporosis) or have a family history of severe bone loss; if you have bone loss (such as avascular necrosis) affecting more than half of your femoral head, you have multiple fluid-filled cavities (cysts) greater than 1 centimeter in your femoral head, a test may be needed to determine your level of bone loss;
- You are a female of child-bearing age;
- Your kidneys are not working very well;
- You have a suppressed immune system due to diseases such as AIDS or are receiving high doses of corticosteroids;
- You are severely overweight; or
- You have had reactions to wearing metal jewelry or have what is called “metal sensitivity.”
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When is a hip replacement a better option?
When a patient suffering from hip pain has one of the conditons noted above, a hip replacement may be the better option. Typically, patients over the age of 55 to 60, unless they are very active and have strong bones, should consider a hip replacement instead of hip resurfacing. Younger patients who are inactive and/or have weak bones should also consider a hip replacement. Keep in mind that hip replacement is an excellent, proven operation that has evolved over the past three decades. If in doubt, choose a hip replacement, since the long-term results of hip replacement are well known, and the procedure is tried and tested.
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Why did hip resurfacings fail in the past?
Early hip resurfacing operations used to fail because of poor materials and design. It is now understood that the loosening and failure of many of the components was caused by polyethylene particles generated from wear of the plastic bearings used in early hip resurfacings. This polyethylene debris caused osteolysis - the degeneration of bone tissue - which can lead to component loosening.
Other types of implants in the past used metal-on-metal bearing surfaces, just as today’s hip resurfacing implants use. However, these devices of the past were subject to early failure due to design flaws and the technological limitations on producing a quality metal bearing surface. Since then, these problems have been overcome.
The development of the current metal-on-metal bearing surface, using highly polished high carbide cobalt chrome, provides a smooth and durable bearing surface that can outlast the lifetime of the patient. Modern hip resurfacing bearings nearly eliminate osteolysis and loosening, the primary causes of hip resurfacing failures in the past. Additionally, our newer, minimally invasive surgical approaches reduce the chance of blodd loss and resulting decay in the preserved femoral ball (“osteonecrosis”) which further contributes to the success of modern hip resurfacing.
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Why is one operation called “total” hip replacement, and the other only a “hip resurfacing”? Is less of the joint replaced in hip resurfacing since the word “total” is not applied to this surgery?
The names of the operations do not imply that less of the joint is replaced with hip resurfacing. More accurately, one operation should be called “total hip replacement” and the other should be called “total hip resurfacing.” In both cases, the “total” hip joint, i.e., all moving surfaces are replaced with new ones. In total hip replacement, a spike (femoral stem) is placed down the hollow part of the thigh bone and a metal ball is attached to this prosthesis. In (total) hip resurfacing, your own ball is ground down, and a properly sized metal cap is used to resurface it, thereby sparing some bone, which is always an advantage. In both operations, the socket is replaced identically. The word "total" could (and should) properly be applied to both operations.
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Who is advertising this procedure and why?
Orthopaedic surgeons, hospitals, clinics, and implant companies who stand to gain from your having surgery will obviously promote this procedure. There is nothing inherently wrong in this, and often valuable information is thus made available to the patient. But keep in mind that those who hype a procedure may not disclose all the information you need to make a sound decision. It is hoped that this material has given you all aspects of the debate, so that rational thinking, proper information, and preparation will allow you to become an active participant in the management of your arthritic hip. We are committed to sharing knowledge and our experience, because well-informed patients make wise choices and have the best outcomes from surgery. Feel free to email our surgeons for more information.
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