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BHR compared with THR
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BHR compared with THR
Hip resurfacing has been developed as a surgical alternative to total hip replacement (THR). The procedure consists of placing a cobalt-chrome metal cap, which is hollow and shaped like a mushroom, over the head of the femur while a matching metal cup (similar to what is used with a THR) is placed in the acetabulum (pelvis socket), replacing the articulating surfaces of the patient's hip joint and removing very little bone compared to a THR. When the patient moves the hip, the movement of the joint induces synovial fluid to flow between the hard metal bearing surfaces lubricating them when the components are placed in the correct position. The surgeon's level of experience with hip resurfacing is most important; therefore, the selection of the right surgeon is crucial for a successful outcome.
The potential advantages of hip resurfacing compared to THR include less bone removal (bone preservation), a reduced chance of hip dislocation due to a relatively larger femoral head size (giving the patient has an anatomically correct femoral head size), and easier revision surgery for any subsequent revision to a THR device because a surgeon will have more original bone stock available The potential disadvantages of hip resurfacing are femoral neck fractures (rate of 0–4%), aseptic loosening, and metal wear. Due to the retention of the patient's complete femoral neck other advantages exist: Surgeon induced discrepancies in leg length (as could happen with THR) are now minimized. Also, the toe-in or toe-out faults that could occur interoperatively with THR are now over because the femoral neck that determines foot direction is left undisturbed with hip resurfacing.
On February 10, 2011, the U.S. FDA issued a patient advisory on metal-metal hip implants, stating it was continuing to gather and review all available information about metal-on-metal hip systems. On June 27–28, 2012, an advisory panel met to decide whether to impose new standards. No new standards, such as routine checking of blood metal ion levels, were set, but guidance was updated.
Patient suitability for hip resurfacing is decided by the patient's anatomy and the patient's surgeon. Hip resurfacing is intended for younger patients who are not morbidly obese, are clinically qualified for a hip replacement (determined by the doctor), have been diagnosed with noninflammatory degenerative joint disease, do not have an infection, and are not allergic to the metals used in the implant. Hip resurfacing should not be used on patients who have severe bone loss in their femoral head, those with large femoral neck cysts present (typically found at surgery) or cysts that are close to the head neck junction, or patients who have poor bone stock or osteoporosis. Caution should be used for patients who have rheumatoid arthritis, are tall, thin, or small boned, those with osteonecrosis (poor blood supply) to the femoral head, or those with femoral head cysts > 1 cm on an x-ray taken before surgery. Metal-on-metal resurfacing systems are generally unsuitable for women of child-bearing age due to unknown effects of metal ion release on the fetus. Patients with any of these conditions may not be suitable candidates for hip resurfacing.
In 2006, the United States FDA approved hip resurfacing using the Birmingham Hip Resurfacing (BHR) system, designed by British Orthopaedic surgeon Derek McMinn. On July 3, 2007, the FDA approved the Cormet hip resurfacing system made in the UK by Corin Group and marketed in the U.S. by Stryker Corporation. On November 9, 2009 the FDA also approved the Conserve-Plus hip resurfacing system made by Wright Medical Technology. There are several other manufacturers of hip resurfacing systems, mainly in Europe. Another THR and hip resurfacing system, the DePuy ASR, which had been undergoing clinical trials for hip resurfacing in the United States and marketed overseas, has been recalled as a result of having been proven to have abnormally high revision rates. A prospective patient, therefore, needs to be cautious to confirm the type of device being used has an acceptable track record. Subtle differences among the devices in terms of design, manufacturing and surgical technique can prove to be detrimental to clinical success.
The hip resurfacing devices are metal-on-metal articulating devices which differ from total hip replacement devices because they are more bone conserving and retain the natural geometry (so-called large ball THR devices share this trait). A THR requires that the upper portion of the femur bone be cut off to accept the stem portion of a THR device. The femur cap of the hip resurfacing devices does not require the femur bone be cut off; instead the top of the femoral head is shaped to closely fit the underside of the cap. Both hip resurfacing and hip replacement require that a cup is placed in the acetabulum of the hip socket. The main advantage of the hip resurfacing surgery is that when a revision is required, there is still an intact femur bone left for a THR stem. When a THR stem requires a revision, the metal stem in the femur has to be removed and often more bone is lost in the process of removal and replacement with a larger diameter stem. Having a hip resurfacing at a younger age means that a revision will likely be easier to perform when required.
Recent studies have shown that the outcome of a hip resurfacing is dependent on surgeon experience and that proper positioning of hip resurfacing components is crucial. Therefore, in addition to ensuring that a proven device is used, patients should take care in selecting a surgeon with experience and a good track record.
Although formal labeling restrictions exist in some countries, including the United States, hip resurfacing may allow younger, active people to return to many activities they enjoyed prior to their hip problems, which is an advantage over a traditional hip arthroplasty. The large size cap and cup of the hip resurfacing devices are the same size as a person's original ball and socket and thus are less prone to dislocation.
An often forgotten but very important advantage of hip resurfacing and thereby the retention of the femoral neck is the fact that hip resurfacing has the least measurable amount of "stress shielding" when compared to any type of THR. This means that with hip resurfacing the femur's upper portion fully retains its natural mechanical characteristics under load, also ensuring less disturbance of the processes that place inside bone that is alive.
There are many athletes with resurfaced hips that continue to compete at the personal and the professional level in a myriad of activities. They include:
In August 2010, DePuy Orthopaedics, Inc., issued a voluntary recall of the ASR™ XL Acetabular System and ASR™ Hip Resurfacing System after new information from the UK National Joint Registry indicated that the number of patients who required a second hip replacement procedure, called a revision surgery, was higher than previously reported data. Potential complications include pseudotumors, metallosis, ALVAL (Aseptic Lymphocytic Vasculitis Associated Lesions), and femoral neck fracture.