While the wear rate with ceramic-on-ceramic total hip replacements is negligible and other problems (including fracture) extremely rare with the use of well-designed components and accurate surgical technique, squeaking in total hip replacements has recently become an issue. Squeaking in total hip replacements is thought to be caused by roughening of the ceramic surface of one or both components, or the presence of 3rd body debris in the space between the ball and socket.

Any impingement between the neck of the femoral component and the ceramic liner of the socket can generate particles of ceramic and/or metal that may lead to squeaking. Partial shucking of the head in and out of the socket may also cause damage to the ceramic surfaces stripe wear. Avoiding these problems is highly dependent on accurately positioning the acetabular and femoral components.

Recently, it has been noted by several authors, including myself, that a particular design of ceramic liner (where the ceramic is protected from chipping by a metal ring which extends past the ceramic) used with a specific femoral component manufactured by the same company has lead to an extremely high risk of squeaking. The squeaking likely occurs due to impingement of the metal femoral neck against the protective metal ring, generating metal debris which enters the interface between the ball and socket and causes a vibration that we hear as a squeak. In my practice, the incidence of significant squeaking in designs without the protective ring is less than 1/2% while the incidence of squeaking in a small group of ceramic hips with this protective ring is >10%, a 20-fold increase. Therefore, many surgeons, including myself, have quit using this acetabular component design.

Ceramic hips require very precise placement of the components to prevent impingement between the femoral and acetabular components. However, if done well, a ceramic hip should wear extremely well without chipping, breakage, or squeaking, and also without the theoretical risks that metal-on-metal hips carry.

Because implant positioning is absolutely critical to the success of a ceramic-on-ceramic total hip replacement, be sure to ask your surgeon how much experience he has with ceramic-on-ceramic hip replacements. Done well, these hips may last your lifetime, even if you are young and active.

Additional reading on squeaking ceramic hips:

• Influences of Prosthetic Design on Squeaking after Ceramic-on-Ceramic Total Hip Arthroplasty AAOS 2009 Poster
• Influences of Prosthetic Design on Squeaking after Ceramic-on-Ceramic Total Hip Arthroplasty AAOS 2009 Handout
• “The Squeaking Hip: A Cause for Concern-Disagrees.” Yang CC et al Orthopedics. 2007 Sep;30(9):739-42
• “Squeaking in a Ceramic on Ceramic Total Hip” Eickman TH et al Proceedings of the 8th BIOLOX Symposium 2003.
• “Squeaking in Ceramic-on-Ceramic Hips; Incidence, Causes and Solutions.” Toole, G. et al 2008.

Since use of the “Capsular Noose” procedure, developed by Dr. Swanson in 2002, and the use of larger femoral heads and lateralized offset stems, dislocation of the artificial hip is very.unlikely. However, during the early post-operative period while soft tissues are healing, you should be careful to avoid extreme positions, especially turning the knee inward when your hip is flexed (such as bending forward while sitting down with crossed legs). Always remember, as long as you can see the inside of the knee on the operated side, dislocation is extremely unlikely, even while bending over.

The physical therapist will teach you stretching exercises to help cross your ankle over the opposite knee for handling shoes, socks, clipping toenails, etc. Always keep the knee rotated outward when you bend the hip past 90 degrees (such as reaching for something on the floor when sitting in a chair).

As a general rule, it is safe to flex the hip past a 90 degree angle if the knee is rotated outward and you can see the inside of the knee—keep this rule in your mind at all times; it will eventually become automatic when you bend over. Additionally, you will be given specific exercises by a Physical Therapist to help strengthen and stretch the muscles around the joint. Do these exercises regularly, at least 3 times daily, during the first 6 weeks after surgery. Stretching exercises are also important, particularly rotating the knee outward. You will be taught to sit in a chair with your feet together and press the knees outward while bending forward a bit. You will also begin to slide the operated ankle up the opposite leg with the knee rotated outward to eventually enable a “figure-4” position to allow easy access to your feet. Remember, as long as the knee is rotated outward, it is very difficult to dislocate the hip.

For more information about the Capsular Noose Repair read Dr. Swanson’s Publications and Presentations

To see a demonstration of post-op exercises and stretches read the Patient Brochure.

Hip resurfacing remains a controversial topic among hip surgeons. While used commonly in some countries in Europe and Australia, other countries such as the United States have been slow to follow suit, largely because of catastrophic results with the earliest designs in the 1970’s and restrictions placed on its use by the FDA. However, two hip resurfacing devices have been approved by the FDA for use in the United States. On May 9, 2006, the Birmingham Hip Resurfacing System (BHR) sold by Smith & Nephew Orthopaedics, and on July 3, 2007 the Cormet sold by Stryker/Corin were approved for use in the U.S. Other companies’ resurfacing devices are sure to follow. But, what is a hip resurfacing anyway, and how does it differ from a total hip replacement?

Hip resurfacing is a type of hip replacement that involves resurfacing the femoral head (hip ball) with a smooth, spherical metal cap (femoral component), similar to the way in which a dentist caps a tooth. If the acetabulum (hip socket) is in good condition, only the ball is resurfaced, and the socket is left alone. More commonly, when the socket is worn, it too must be resurfaced with a smooth, artificial metal socket (acetabular component). This contrasts with the surgical technique used in conventional total hip replacement which removes the worn out ball and replaces it with an artificial ball attached to a stem anchored inside the hollow femur (thigh bone). The artificial socket for both total hip replacement and resurfacing replacement are very similar, although resurfacing sockets are always made of metal while total hip replacement sockets may use metal, ceramic, or plastic (polyethylene).

So what are the advantages and disadvantages of a resurfacing replacement vs. a total hip replacement?

Advantages:

1. Bone Preservation

Bone preservation is often noted as one of the main advantages of hip resurfacing. Because the femoral head is resurfaced rather than removed, some of the ball is left intact, and the femoral canal is left untouched for the most part, thus preserving femoral bone. While conserving bone on the femoral side, some resurfacing hip sockets require that a bit more bone be removed from the acetabulum than in a conventional total hip replacement to allow the resurfaced femoral head to fit within the socket. Recently, manufacturing companies have begun addressing this issue by producing thinner acetabular shells for their resurfacing prostheses. Most important, proponents of hip resurfacing stress that because the femoral head has not been removed and the femoral canal has been left largely untouched, when it comes time to revise the prosthesis, it can be done very easily because of minimal bone loss.

2. Less Stress Shielding

“Stress shielding” refers to bone loss (osteoporosis) caused by lack of use of certain parts of the body’s skeleton. The resurfaced hip replacement more closely approximates a natural hip because the upper femur is largely left intact and therefore sees stresses that more closely resemble those in a normal hip than does the femur after a total hip replacement. Many advocates of resurfacing say that bone density at the head/neck junction (just at the base of the hip ball) is maintained and, in many cases, increased with use of the hip, although not all studies agree. However, although the real answer may not be entirely clear, it stands to reason that the more naturally the hip is loaded, the more likely stress shielding will be minimized.

3.Low Dislocation Rate

Dislocation of a hip prosthesis is in part related to the size of the ball and socket used. The larger the ball and socket, the less likely the hip will dislocate. Because a resurfacing prosthesis mimics the size of the natural ball and socket, it is less likely to dislocate than the ball and socket used with many total hip replacements, which may be only 1/2 – 2/3 the size of the natural hip ball. However, with newer instrumentation for standard total hip replacement allowing more accurate placement of components, use of larger balls and sockets, and better soft tissue repair techniques (see Capsular Noose page), dislocation even after total hip replacements is becoming quite rare.

4. Ability to Resume Athletic Activities

Hip resurfacing is often uplifted as a panacea for athletes wanting to return to high-impact sports due to its metal on metal wear resistance and low dislocation rate. Some also assert that patients with resurfacings vs. total hip replacements claim they are better able to return to competitive sporting activities, although the literature is not clear on this point. However, contrary to what some might say, hip resurfacing is not without risks if subject to high-impact activities.

“Endorphin junkies are fooling themselves if they believe bionic parts–no matter how sturdy they seem–give them license to resume high-impact activities such as running, basketball, and singles tennis.” warns Richard Laskin, MD, chief of the Division of Arthroplasty, Hospital for Special Surgery.

“I don’t like them doing high-impact things,” says Ronan Treacy, an orthopedist who helped develop the Birmingham metal/metal resurfacing hip Replacement, “but the fact is, most people ignore their surgeon’s advice.”

At a time when total hip replacements totally relied on polyethylene sockets (which are much less wear-resistant than metal) and when dislocation was much more common with athletic activities, this theory made some sense. However, total hips now utilize metal-metal and ceramic-ceramic articulations which provide tremendous longevity even in young, active patients, and cementless fixation provides for survival of the standard total hip replacement which may outlive even young, active patients. In contrast, the currently available resurfacing head is cemented into place, so there is technically even more reason to avoid impact loading activities – because these activities tend to crack the cement and lead to earlier loosening. Whether or not the various resurfacing devices will actually hold up to repetitive high-impact exercise is unknown because of a lack of long-term data. What is known is that all cemented implants eventually loosen, so it stands to reason that subjecting any cemented implant to high-impact loading stresses will lead to earlier loosening and need for revision surgery.

Disadvantages:

1. Early Failures

The biggest disadvantage of hip resurfacings is that the early failure rate is much higher than that after total hip replacement. Although in the innovators’ hands, failures are less likely, the risk of a femoral neck fracture (the ball breaking off of the femur bone) in the first year is significant, as high as 3% or more. Fractures are often related to surgeon error, most commonly notching of the femoral neck or placing the artificial ball in a position which is too low (called “varus malpositioning.”). An additional factor may be disruption of the blood flow to the remaining femoral head, a condition known as avascular necrosis. A review of the published literature shows that the short term survival rates with resurfacing replacements vary from 75-100% while most well-designed total hip replacements have short and mid-term survival rates exceeding 95%, even in young, active patients.

2. Late Failures

Just as disconcerting are failures occurring more than 5 years after implantation. The BHR femoral head prosthesis must be cemented in place while the socket is cementless. All cemented components will eventually loosen. So given enough time, all cemented resurfacings, just like cemented total hips, will loosen and fail, guaranteeing a second trip to the operating room for revision surgery at some point in young, active patients. In contrast, many cementless total hip replacements may remain intact indefinitely. Therefore, using the currently available cemented resurfacing prosthesis in a young, active patient, although conserving bone for a future revision, ironically almost guarantees that a revision surgery will be necessary at some point due to loosening of the cement. In contrast, using an entirely cementless total hip replacement could potentially last a lifetime, even in a young, active patient.

3. Surgical Procedure

Resurfacing hip replacement requires a larger surgery with a more invasive surgical approach than conventional hip replacement because the femoral head must be preserved and moved out of the way to visualize the hip socket. Resurfacing incisions have historically been 8-12 inches in length, although recent advances in surgical technique have allowed them to be performed through more conservative approaches. In addition, resurfacing patients occasionally are required to be on restricted weight-bearing using crutches for 6 weeks post-operatively. In contrast, conventional total hip replacement can be done through a minimally invasive, muscle sparing, 3-4 inch incision, and patients are allowed to walk on their new hip fully weight-bearing immediately. Although bone preservation is attractive, minimizing muscle trauma and scarring is also important to allow a rapid recovery and minimize complications.

4. Metal/Metal Wear and Toxicity

Probably the most disconcerting yet still uncertain potential complication of any metal-on-metal replacement is metal ion toxicity. Conventional hip replacements can utilize a variety of bearing surface combinations including metal-metal, ceramic-ceramic, metal-polyethylene, and ceramic-polyethylene. Polyethylene may be either standard or highly crosslinked (a more durable form of polyethylene). Resurfacing prostheses today are only able to utilize a metal femoral cap paired with a metal acetabular socket, although eventually other bearing surfaces will likely become available.

Although the wear rate of metal against metal is extremely low, the metal particles generated often lead to elevated levels of cobalt and chromium ions in the bloodstream and body tissues. Additionally, all metal ions must be filtered and removed by the kidneys. The graph below illustrates the volume of particles generated by various bearing surfaces (from Greenwald & Garino, JBJS, 2001):

Although many experts fear a possible carcinogenic effect from these high metal ion levels, no long-term study has confirmed this potential risk. However, ridding the body of these ions may be a problem in a patient who has kidney problems, so patients with kidney disease or a history of kidney problems in the family should probably avoid a metal-metal hip replacement or resurfacing. Additionally, women of childbearing age should probably avoid metal/metal bearings because of potential toxicity to a fetus from the wear debris.

An additional type of metal toxicity known to occur around metal-metal replacements is a type of allergic reaction, called a “hypersensitivity reaction.” Local and systemic reactions to metal particles have been documented, most commonly an inflammatory reaction adjacent to the prosthesis that leads to bone loss called “osteolysis” (i.e. ”dissolving bone”). Osteolysis around the metal prosthesis will eventually cause weakening of the bone and loosening of the prosthesis or fracture of the bone.

5. Inability to Use with Deformity or AVN

Because resurfacing arthroplasty only caps the existing anatomy, it cannot be used in cases of deformity of the femoral head, such as with Perthes disease, Slipped Capital Epiphysis, or high grade Dysplasia of the hip. Additionally, its role in a condition known as Avascular Necrosis (AVN) is not well defined, and resurfacing often cannot be used when the area of blood loss to the femoral head is large. Many young patients develop arthritis due to one of these conditions. However, resurfacing arthroplasty should not be used in these conditions because it cannot restore the leg’s normal length or the mechanics of a deformed hip joint as can be done with total hip replacement.

Summary

Although metal-metal resurfacing hip replacements may be the right choice for many young, active individuals, it is not the panacea that many advertising campaigns have made it out to be. The resurfacing arthroplasty may be used by some surgeons to promote their practices, in spite of the fact that much is still unknown about the long-term results of this procedure. In fact, favorable studies exceeding 5 years are rare in the published literature. In contrast, favorable studies of total hip replacements up to 25 years and longer are available in the peer-reviewed literature. Additionally, as with total hip replacements, favorable results with one design of resurfacing arthroplasty do not guarantee favorable results with another brand of resurfacing device.

On the other hand, with further study and advances in technology, this type of replacement may hold much more promise in the future. Better metal alloys, manufacturing processes, surgical techniques, development of cementless femoral fixation, and use of alternative bearing-surface materials such as ceramics may ensure more durable, long-lasting results even in young, active patients, without the risk of early failures, loosening, metal ion toxicity, or other complications. So, just as with all other new technologies, Caveat Emptor (“Buyer Beware”).

For more information about resurfacing visit the Link Library.

Total hip design has come a long way since Sir John Charnley’s original cemented hip in the late 1960’s. Cement has largely been replaced with cementless (bony ingrowth) technology, plastic sockets are being replaced with highly crosslinked polyethylene, ceramics, and metal, and femoral stem shapes continue to evolve.

Some long stem femoral components cause problems including “stem tip thigh pain,” difficulty if removal is ever required, and stress-shielding (osteoporosis) of the upper femur which does not see the normal weight-bearing forces when part of the body weight is carried by the lower tip of the femoral component. Sometimes, the upper part of the femur literally melts away when a long stem femoral component is used.

One of the advantages of a resurfacing arthroplasty (where the ball is resurfaced with a metal cap rather than replacing it with an artificial ball anchored by a stem down the center of the femur) is that it loads the femur more effectively, reducing the risk of stress-shielding bone loss.

Another total hip design which is gaining popularity is the short femoral stem. With improvements in bony ingrowth technologies, much shorter femoral components can now achieve stable fixation to bone. Shorter stems will result in loading of the femur from top down reducing the rate of stress shielding and bone loss. It is likely that the next new step in design technology is the use of shorter and shorter femoral components.

Click for Full-size Image

Leg length discrepancy is one of the most common complications after total hip replacement. A hip which has become arthritic is almost always short because it has lost the cartilage space of the joint, often resulting in shortening of the limb 3-5mm (1/8 – ¼ inch). Most often, we try to lengthen the hip this amount to equalize the leg lengths.

Sometimes, the leg must intentionally be over-lengthened; for instance, if the soft tissues are so lax that the only way to tighten the hip up to prevent a dislocation is to add length to the leg. However, with lateralized (high offset) femoral components and larger femoral heads, this is less often needed today. More often, the leg is inadvertently over-lengthened (or occasionally shortened). This is a known, accepted potential complication of total hip replacement, and discrepancies of up to ½ inch are considered within the accepted standard of care.

However, although most patients tolerate leg length discrepancies of up to ¼ inch quite well, ½ inch leg length discrepancies (or more) are not often well tolerated, and most will need a shoe lift on the opposite side to allow comfortable walking. Therefore, many methods to try to ensure equal leg lengths after total hip replacement have been devised and utilized over the years.

In 1997, we began working on a technique utilizing careful pre-operative templating to equalize leg lengths on the x-ray, then duplicate these measurements intra-operatively to attain equal leg lengths. However, no matter how carefully the x-rays were templated and the surgery performed, several patients still had over-lengthening of the leg without a good explanation.

A few years ago, we began looking critically at our x-ray templating to try to find the source of error. In the process, we began templating the NORMAL hip along with the ARTHRITIC hip. We soon found that if we used the x-ray templating of the NORMAL hip intra-operatively, we were more likely to achieve equal leg lengths. Since then, we have observed this to be true in approximately 75% of our patients.

We have now conducted a radiographic study scientifically showing that using templating measurements from the normal hip routinely gives more accurate restoration of equal leg lengths than using measurements from the arthritic hip. Utilizing this technique, we can equalize leg lengths to less than ¼ inch difference in almost all patients. Of course, we still see exceptions; for instance, when the soft tissues are so lax that the only way to reduce the risk of dislocation is to intentionally lengthen the leg, or when a large pre-existing leg length discrepancy exists, making accurate correction much more difficult.

Eventually, even more sophisticated methods of restoring equal leg lengths will be developed, particularly with the development computer navigation systems for total hip replacement. Technology will continue to move forward and minimize the problem of leg length discrepancies after total hip replacement. For now, we can come extremely close using these new templating techniques.

Research on Advantages of Minimally Invasive Hip Replacement (Read PDF)

The Capsular Noose Research (Read PDF)

Literalized Offset THA (Read PDF)

JMB Contralateral Template Abstract (Read PDF)