Total hip resurfacing has been a popular subject for young, active patients with osteoarthritis of the hip. The fundamental ideas behind the procedure include preservation of the femoral bone stock, low wear rate and low dislocation rate. The ideal candidate is a male under 55 years with good bone quality and normal hip geometry. Patients with large limb length inequality are not good candidates. Hip resurfacing simply places a metal cap over the femoral head as opposed to removing the femoral head in total hip replacement. This allows for easier revision surgery in the future if needed. This is the advantage for young patients whom revision surgery is a strong possibility. There have been some studies reporting more natural gait patterns and faster walking rates in patients with hip resurfacing compared to total hip replacement. There are no restrictions placed on patients who have hip resurfacing and they are allowed to return to all activities including sports.
The low wear rates of the implants are due to the metal on metal bearing articulation. The advantage of metal on metal is the extremely low wear rate. It is unlikely that the bearing surfaces with metal on metal will wear out. Failure of the implant will be based on loosening of the bone ongrowth and not wear of the implant. The disadvantage is that cobalt and chromium ions are absorbed into the blood stream from the implants. There have been no confirmed problems with elevated levels of cobalt and chromium and they do not reach toxic levels. Women of
childbearing age are traditionally not candidates for hip resurfacing because the metal ions cross the placenta, but there are many young women who have hip resurfacing because of their age. Some of these women have given birth in the United States and no problems or birth defects have been reported. Patients with chronic kidney failure are also not candidates as the kidneys help to clear these ions from the blood stream.
The disadvantages of hip resurfacing are increased surgical complications and unknown longevity. We currently only have data out to 10 years on the Birmingham Hip Resurfacing device which was FDA approved in the United States in 2006. It is unknown how long these implants will last and with the current 10 year follow up data, hip resurfacing has been shown to be as good as hip replacement, but not better. The surgery itself is somewhat more difficult than standard hip replacement and involves larger incisions and increased soft tissue dissection. The Birmingham Hip (Smith and Nephew) and the Cormet 2000 (Stryker) are currently the only 2 FDA approved hip resurfacing implants in the United States. The FDA currently mandates that surgeons be formally trained with each implant system before they are allowed to use them.
The anterior approach is an extremely uncommon approach used for hip resurfacing. There are only a handful of surgeons in the United States capable of performing hip resurfacing through this approach. The anterior approach offers the advantage of decreased soft tissue dissection and a smaller incision. The typical incision for anterior approach hip resurfacing is 5-6 inches. One potential complication of posterior approach hip resurfacing is sciatic nerve palsy which results in numbness and a drop foot. This complication is not seen with anterior approach because of the difference in leg positioning for the exposure. Anterior approach hip resurfacing is performed with the use of x-rays in the operating room. This ensures that the cap is centered precisely on the femur and the cup is positioned correctly in the pelvis. The longevity and survival of hip resurfacing has been shown to be directly related to implant position, so this is a considerable advantage of performing the surgery through the anterior approach.
Dr. Yerasimides’ view on Hip Resurfacing
Although hip resurfacing is currently unproven long term and has more associated complications, it does provide advantages for the young patient in which revision is likely. My major objection to the surgery had been the large posterior approach used by almost all surgeons who perform hip resurfacing. The incision is typically 12-16 inches and involves extensive soft tissue and muscle dissection. I am a firm believer in preservation of the soft tissue and muscle envelope around the hip and therefore had been reluctant to perform the surgery. More recently however, I have performed the surgery through the anterior approach. I believe this gives the patient the advantage of bone preservation with hip resurfacing along with muscle preservation from the anterior approach. This combination, I believe, will enhance the benefits of the procedure.
