The BIRMINGHAM HIP Resurfacing arthroplasty (BHR) is a newer development in hip replacement surgery developed by Derek McMinn and Ronan Treacy in Birmingham, England. They started experimenting and developing this technique in 1991. Early efforts were focused on the best design and fixation techniques. They have been using the BHR arthroplasty in its current form since 1997. This procedure has been widely used in England, Belgium, and other parts of Europe since 1997. It was introduced into Canada in 2003. It was only approved by the FDA for use in the United States in May of 2006.
The major difference between the BHR arthroplasty and a conventional hip replacement is the BHR procedure preserves most of the bone of the femoral head. In conventional hip replacement surgery, the femoral head and a portion of the femoral neck are completely removed and replaced with a stemmed prosthesis which is inserted into the medullary canal of the upper femur. The BHR procedure shapes the femoral head and recaps it with a metal surface replacement. This preserves the normal bone of the upper femur and allows normal mechanics and weight-bearing loads across this area. Normal load forces through the bone of the upper femur keep the bone healthy and strong.
The acetabulum (cup or socket) of the hip joint is also resurfaced. The socket is reamed to a specific size and shape, and a thin-walled metal cup is inserted. The acetabular component has a rough, beaded back surface. The patient's bone grows into this surface, producing biological fixation of the acetabular component. No cement is necessary for fixation of the acetabular component. The large femoral head resurfacing and the thin-walled metal acetabular lining more anatomically reproduces the normal hip anatomy and mechanics. The larger femoral head size reduces the risk of dislocation and produces a more natural feel to the hip.
Resurfacing arthroplasty of the hip is not a new idea. It was initially developed in the 1970s. The early head resurfacing designs were similar to the BHR. However, the acetabular component was made of polyethylene (plastic) and was cemented in place. By necessity with the large head size, the polyethylene acetabular components were thinly walled. The combination of thin plastic and cemented fixation led to a high early failure rate. The procedure was largely abandoned until it was resurrected by Dr. McMinn in England and Dr. Harlan Amshutz in California. Improved metallurgy and manufacturing techniques have promoted the development of the metal-on-metal bearing surface used in the modern resurfacing arthroplasty.
The BHR arthroplasty is primarily indicated for the younger, active patient. Good quality bone is a firm requirement for this procedure. Most patients suitable for this procedure will be under 60 years of age. The metal-on-metal bearing surface gives a more durable articulation, and the larger head sizes decrease the risk of dislocation. This allows patients to return to a more vigorous lifestyle and a higher level of sporting activity that is generally recommended for conventional total hip arthroplasty.
Bone quality generally deteriorates with age. For patients with borderline bone quality, I recommend a bone density test as part of your evaluation for a BHR. Bone density results are reported as a T-score. A bone density of less than –2.0 is a definite contraindication to resurfacing arthroplasty. A bone density of between –1.5 and –2.0 is a borderline contraindication.
The metal-on-metal articulation has advantages and disadvantages. The metal is an alloy made of cobalt, chromium, and nickel. It can be manufactured to a hard, smooth, durable surface. It has replaced the traditional metal-on-polyethylene bearing surface used for many years in conventional hip replacement surgery. It is extremely unlikely to break or wear out. However, microscopic wear of the metal does occur and produces elevated levels of cobalt and chromium ions in your blood and urine. The levels gradually increase for approximately the first 6 months while the metal surfaces "wear in." They remain stable after that. Metal-on-metal bearing surfaces have been used in hip replacement prostheses since the 1960s. There are no known medical complications or consequences of these elevated cobalt or chromium levels. They are not associated with an increased risk of cancer or leukemia. However, the risk to a fetus is unknown at this time. It is recommended that a metal-on-metal bearing surface not be used in women still wishing to bear children.
The most common diagnosis for patients undergoing a BHR is osteoarthritis or degenerative arthritis. It is also very suitable for arthritis caused by avascular necrosis, although enough healthy bone must still be present to support the resurfacing. It may also be suitable for patients with hereditary hip dysplasia which has developed into painful arthritis. In patients with severe deformity from hip dysplasia, conventional hip replacement may be a better option. It is also commonly used for post-traumatic arthritis (arthritis which developed after an accident or injury). It is generally not recommended in patients with rheumatoid arthritis.
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