• History
• Benefits
• Metal-on-Metal Hip Resurfacing
• Advantages of The Birmingham Hip Resurfacing
• Special Risks of Hip Resurfacing
• Special Requirements of Resurfacing Patients
• Risks and Potential Complications

History
Hip resurfacing has evolved over the past decades with advances in design, metallurgy and surgical techniques. Sir John Charnley carried out the first Hip Resurfacing in the 1950's. Teflon components were used, which unfortunately wore out within two years of implantation. This failure of materials plagued the orthopedic community for several decades. The 1970's was the next significant development of hip resurfacing, with the usage of metal femoral heads, with polyethylene acetabular cups which were fixed with cement. About 55% of these resurfacings failed within 6 years after implantation due to excessive wear of polyethylene.

In 1990, Derek McMinn and Ronan Treacy of the Royal Orthopedic Hospital at Birmingham pioneered the metal-on-metal resurfacing prosthesis called the Birminhgam Hip Resurfacing (BHR) Prosthesis composed of Cobalt Chrome at both Femoral and Acetabular sides.

Unlike conventional Total Hip Replacement (THR), hip resurfacing is conservative in that the femoral head and neck of the hip joint are not removed nor is bone removed from the femur. In the case of surface replacement, less bone is also removed from the acetabulum as compared to conventional THR since no polyethylene liner is used.

X-ray (left), showing post-BHR procedure where the femoral head is reshaped to accept metal cap with small guide stem. Head size is about 50 mm in diameter. Metal cup is set into pelvis. As a result, the femoral bone is loaded more like a normal hip and the bone is preserved. Since the resurfaced head is very similar in size to the normal hip (about 40-50 mm), it is more stable and dislocation risk is minimal. An example of a surface replacement is shown in Figures 6a and 6b.

Several different hip resurfacing systems were introduced in five countries in the early 1970s. They were implanted in young patients who were expected to require more than one replacement in their lifetime because they were thought to be more conservative devices than the conventional replacements. Some surface replacements with polyethylene have had long-term durability of up to 18 years thus far. However, because of the large diameter ball size of the surface replacement, there was more polyethylene bearing wear (the debris accumulation which undermines the fixation) which results in loosening of the prosthesis. Most surgeons abandoned surface replacements with polyethylene in the 1980s and early 1990s. Despite the fact that the durability was often less than desired, the femoral bone preserved by these systems was especially valuable for these young patients when revision surgery was required making that second surgery comparable to primary replacement.

The conservative and more physiologically compatible nature of the surface replacement has always been appealing to both surgeons and patients. There is renewed interest which has been fostered by the reintroduction of all-metal bearings which could dramatically increase the durability. The first of these metal/metal surface replacements was introduced in Germany and subsequently in England and at the Joint Replacement Institute (USA) in the early 1990s. The instruments and design have been improved using modern techniques to further reduce wear and to facilitate the procedure. The major advantage of the surface replacement is in the preservation of the femoral head and neck. Further, unlike the acetabular reconstruction with the earlier designs which contained polyethylene bearings, very little bone is removed and the procedure is now conservative on the acetabular pelvic side of the joint as well. In short, no "bridges are burned" with the surface replacement procedure.

Surface replacement may also permit higher levels of post- surgery activity with fewer downside risks than does a stem-type device. The increased stability is particularly conducive for sports and work activities where a more normal range of motion of the hip is required.

The lessons that we have learned regarding design and technique issues during the past 25 years combined with the modern precision manufacturing of metal/metal bearing surfaces have led to a very much improved device. Although it is impossible to predict how much increased durability will be achieved, the volumetric wear reduction is substantial, and it is unlikely that these devices will "wear out". We also believe that the metallic wear debris, based on our histological observations to date, appears to be well tolerated in the tissues. Potential long term undesirable consequences of these devices are unknown. However, they have been successfully implanted for over thirty years so we believe the risk is minimal.

Benefits
Following total hip replacement, joint surfaces will again be smooth and slide easily. This gives most patients pain relief, an increased range of motion, and unlimited walking ability. You may be able to take part in physical activities which before surgery were impossible. However, your hip will not be normal - remember that you will have a prosthetic joint!

An incision is made into the buttock and access is gained to the hip joint. The prosthesis chosen is the one closest possible to the normal size of the hip (small people have small joints and large people have large joints, as you would expect). Great care is taken to keep the wound as small and as neat as possible.

The reason such careful attention is paid to the size of the replacement part is because it means there will be less chance of dislocation, the risk being very minimal anyway (less than 1%), which decreases over time and by six weeks post-surgery this risk is really quite insignificant.

The difference between a total hip replacement and a resurfacing procedure is that a total hip replacement is a much more invasive operation in that the top of your femur, or thighbone, the size of a golf ball, has to be removed so that the prosthesis, or false joint, may be fitted. When a resurfacing is performed, the arthritic bone is simply shaved away and the new ball and socket, or prosthesis, is fitted over your existing bone and cemented into place.

Metal-on-Metal Hip Resurfacing
Cobalt-chrome cast parts. Parts are precision machined to fit each other with small space for body fluid to lubricate. The backside of the cup has a roughened surface to allow bone to grow into implant.

Advantages of The Birmingham Hip Resurfacing

• Femoral head is preserved.
• Femoral canal is preserved and no associated femoral bone loss with future revision. Also, the risk of microfracture of femur with uncemented stem implantation is eliminated.
• Larger size of implant "ball" reduces the risk of dislocation significantly.
• Stress is transferred in a natural way along the femoral canal and through the head and neck of the femur. With the standard THR, some patients experience thigh pain as the bone has to respond and reform to less natural stress loading.
• Use of metal rather than plastic reduces osteolysis and associated early loosening risk.
• Use of metal has low wear rate with expected long implant lifetime.

Special Risks of Hip Resurfacing

• Lack of long-term track record. Current device has only been used for about 7 years. Despite known low wear rate, longevity and longterm effects of wear debris are unknown.
• For some surgeons, the procedure has a longer surgical time. The procedure requires somewhat more skill of surgeon.

Special Requirements of Resurfacing Patients

• Solid bone in femoral head to hold resurfacing component. A few cysts or slight AVN collapse may be acceptable.
• Healthy kidneys to process any blood borne metal ions from debris products.

Risks and Potential Complications
All surgeries have risks, so the potential benefits must be carefully weighed. Some complications are related to the surgical procedure and some are related to the delicate balance of the body which is altered during the operation.

Potential complications of any surgery include: the risks of anaesthesia, bleeding, infection, blood clots, and death. With modern techniques, the risk of anaesthesia related complications is very low. Epidural anaesthesia (which numbs your legs) has the advantage of enhanced post operative pain relief and potentially less blood loss. If a blood transfusion is required, there is a potential risk for a transfusion reaction or disease transmission (e.g. hepatitis), and therefore, autologous blood (your own) is preferred. Prophylactic antibiotics, strict sterile technique, and a special airflow system are used to help prevent infections which occur in less than 1% of cases.

Leg elevation, elastic stockings (TED stockings), ankle exercises, and Coumadin (blood thinning medicine) are used to help prevent blood clots. Tables 1 and 2 below list factors which can increase or decrease the risk of thromboembolic disease (blood clots). A thorough medical evaluation is required prior to surgery which can help identify other potential medical problems and, thereby, minimise those risks.

Potential complications which are related to hip replacement surgery include: a slight dissimilarity in length of the operated leg (inability to fully restore all of previous lost length or over-lengthening), dislocation of the hip, wear and/or loosening of the prosthesis (this is related to activity level), and growth of excess bone around the joint called "heterotopic bone" which can cause stiffness and occasionally pain. An anti-inflammatory medication such as Indocin can be used to prevent or minimize the risk of heterotopic bone. Although rare, there can be problems with healing the trochanter (a bony prominence which is infrequently removed during surgery to obtain better access to the hip joint), fracture of the bone (more common with the porous or press-fit type prosthesis), and nerve injury which can cause muscle weakness in the leg or foot.

The bone ingrowth implants may develop long-term problems related to the bone junction with the porous ingrowth areas, such as corrosion, or problems of bonding of the irregular porous layers to the components. Rarely have the implants broken. Annual follow-up visits will enable us to carefully evaluate and treat any early warning signs of problems. Our experience is based on over 4,000 total hip replacements performed since 1970 and these results are continually updated. As a result, your surgeon has experience with the types of complications which can occur and he or she is making every effort to minimize them. The patient's cooperation is very important in helping to minimise complications by banking blood (autologous)preoperatively, receiving antibiotics in the hospital to minimise infection, taking prophylactic anticoagulants,and wearing elastic "TED" stockings during and after hospitalisation to minimise blood clots.

Sepsis
Patients who have had infections of hip joints may be advised to have delayed reinsertion of a total hip replacement (two operations: one for removal and one for reinsertion of the implants); or direct exchange which involves thoroughly removing the infected implants and tissue and reinserting a new implant at the same operation. While the success of these procedures has continued to increase, special precautions are recommended. These include careful monitoring and close observation in the postoperative period because there is a risk for the recurrence of infection.

Revision Hip Surgery
Increasing numbers of patients are undergoing revision surgery. The most frequent cause of failure of a total hip replacement is loosening of the implant in bone which may be caused or aggravated by the wear process. The magnitude of the surgery depends on the complexity of prosthetic removal and restoration of bone deficiency. Revision of a surface replacement is likely to be less formidable because the femur or thigh bone is intact. Revision surgery may require bone grafts from your pelvic area and/or from the bone bank. Custom prostheses may be needed. Like primary surgery, the durability is dependent upon the techniques utilized and revision surgery is technically more difficult although quality results can be achieved. Third and fourth revisions have also been performed. Once again, each revision may have special and more difficult challenges for the surgeon and the patient. Special precautions are mandatory following these types of procedures.

There are alternatives to total hip replacement surgery. Feel free to learn about the following options :

• Conservative Management
• Femoral Osteotomy
• Arthrodesis
• Pseudarthrosis

Conservative Management
One alternative is to not have an operation. If your pain can be controlled with medication so that you are sufficiently comfortable and you are content with your present activity level and motion in your hip, then you may decide to wait.

Femoral Osteotomy
For patients with developmental dysplasia of the hip (DDH), cutting the thigh bone (femoral osteotomy) or pelvis (Chiari osteotomy) in order to realign the hip may be indicated if the hip weight-bearing area can be broadened or made more congruent. This is often useful in young patients. Recovery following osteotomy may be longer than with joint replacement.

Because of its known unpredictability, femoral osteotomy has been less popular in the United States than in Europe, but it has the advantage of not requiring artificial joint-bearing materials.

Arthrodesis
Arthrodesis is rarely performed, but is an especially effective procedure for younger patients, particularly those who are of short stature and who are otherwise healthy. "Arthrodesis" relieves pain by fusing the femoral head to the acetabulum. It has none of the limitations that a joint replacement or other procedure has in terms of restrictions on activity level. If the patient's back is mobile and without symptoms, it is a very worthwhile procedure. The procedure generally requires internal fixation with a plate and screws and occasionally cast immobilization while healing takes place. An arthrodesis can be converted to a total hip replacement at a later date.

Pseudarthrosis
A pseudarthrosis (Girdlestone operation) involves removing the femoral head without any replacement. The procedure is performed for hip infections and when the patient's bone stock is inadequate for another reconstructive procedure. This leaves the patient with a leg which is shorter and usually less stable (although the changes are less apparent following a resurfacing failure as compared to total hip failure). After this type of operation the patient almost always needs to use at least one crutch especially for long distance walking.

To assist your Surgeon in selecting the most appropriate method of treatment, additional studies may be required on hospital admission.

• Aspiration and Arthrogram
• Radionuclide Scans
• MRI
• CAT Scan
• Bone Densitometry

Aspiration and Arthrogram
Aspiration is desirable to obtain information about the presence or absence of infection, particularly if you have had previous surgery. The surgeon may be able to aspirate fluid directly from the hip joint which will provide valuable information. Final culture results are usually available in 7 - 10 days. On occasion or if a second aspiration is needed, the procedure may be done in Radiology by a radiologist who, at the same time, may perform an Arthrogram (insert dye into the hip joint) to outline the cavity surrounding the joint itself. In general, these procedures are not painful, although local anaesthesia is utilized in the skin. On occasion, mild discomfort may be associated with the study. Most often it is transitory and usually can be relieved by medications. These tests have been most helpful in ruling out or establishing the presence of infection, and in some cases, outlining the areas of loosening.

Radionuclide Scans
If there is a concern about infection, you may be scheduled for an Indium-111 Radioisotope Scan. This requires removing some of your own blood and labelling it with an isotopic material (Indium-111) which is then re-injected. You will return one day later and the area of the joint will be scanned. This procedure is sometimes used in combination with other more routine types of scanning agents so as to evaluate patients with infection or sepsis.

All of the isotopic agents are relatively innocuous. The amount of radiation is generally not much more than a single x-ray exposure. Complications have been minimal. Computerized scanning is sometimes combined with injection of these agents to better define the changes in a three-dimensional way.

MRI
Magnetic Resonance Imaging is a special study that uses a large magnetic field and radio waves to obtain images of the inside of the body. This technique may be useful in evaluating the soft tissues around the hip or detecting the early stages of osteonecrosis. It cannot be used if you already have a hip replacement.

CAT Scan
A CAT scan (computerized axial tomography) is a specialized x-ray scan that can provide additional information about the anatomy of the pelvis or thigh bones and the amount of bone stock available. It is frequently necessary in such conditions as congenital dysplasia, Legg-Perthes disease, or osteonecrosis, or if a custom-type prosthesis may be needed.

Bone Densitometry
Your bone changes in quality and quantity with increasing age (osteoporosis) and also in response to an implant. Bone densitometry is a new technique which can more accurately quantify these changes.