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Effect of Hip Replacement Design in Reducing Hip Dislocation

Hip dislocation can occur after a total hip replacement. The joint may be new, but problems can still come up. In fact, dislocation is the second most common reason why patients have a second hip operation after a joint replacement. Loosening of the implant is the first.

Dr. Barrack, MD, a professor at Tulane University School of Medicine, studied causes of hip dislocations. He looked at implant design and positioning because these are two factors doctors can control. This article gives a summary of recent findings.

Each implant has two parts: the femur (thighbone) and the acetabulum (cup or socket). The shape of each piece and placement in the hip affect motion. Certain types of implants give better motion with less risk of dislocation.

A circular-shaped neck in the femoral implant decreases motion. It's best to use a trapezoid shape (two sides that are parallel to each other). Using a larger head improves motion and gives a more stable joint. There may be slightly more wear with a larger head size.

Researchers using computer modeling show the best angle and position for both parts of the implant. The acetabular cup on the socket side can be turned to match the angle of the femur. The result is a more stable hip joint with less chance of dislocation.

The goal of many studies is to find a hip joint replacement that won’t dislocate. This is difficult given the large number of implant types to choose from. The author offers orthopedic surgeons helpful information when choosing design and position of implants for patients.

References: Robert L. Barrack, MD. Dislocation after Total Hip Arthroplasty: Implant Design and Orientation. In Journal of the American Academy of Orthopaedic Surgeons. March/April 2003. Vol. 11. No. 2. Pp. 89-99.

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