The hip, like the jaw joint, is a ball-and-socket joint. The shaft of the femur (thigh bone) has a spherical top, like a knob, which fits neatly into a concave area of the pelvic bone (hip bone) known as the acetabulum. When we put our hands on our hips, that is not the hip joint; it’s the top curve of the pelvic bone. The hip joint is below that and further inside the body.
The two bones do not rub directly against each other. There is a lubricating fluid known as synovial fluid produced by a membrane in the joint, which smoothes the movements of the bones against each other. There are also several ligaments over the joint, tough connective tissue that runs between bone and bone and gives protection to the joint.
When is a hip replacement necessary?
As we age:
• Our bones become more brittle and a fall can break them. The femur can fracture in its neck, the thinner part just before the knob, and in other places, and the knob may have to be replaced.
• The synovial membrane and its fluid can become thinner and drier, causing pain when the bones move against each other.
• Hip replacement parts wear out in somewhere between 10 and 20 years. A revision surgery is needed to replace them.
Hip implants recalled
In a hip replacement, the pelvic bone may need an artificial lining for the femur to move against, and these can be implanted. Sulzer Orthopedics, Inc. is a company that designs, manufactures, and distributes such implants, as well as others for shoulder, elbow and knee replacements.
One of its products, the “Inter-Op™ acetabular shell” is an artificial lining for the pelvic bone, designed to receive an artificial knob attached to the top of the femur to replace the natural one. This product was recalled in 2001 because of some reports that it had come loose after the surgery was finished. An oily lubricant had prevented it from bonding with the hip bone. About 2,400 people who had this product in their hip replacement later had revision surgery to remove it and use another product. This recall situation was legally resolved recently.
Another recall happened last month, January, 2008 – two Trident hip implant components made by the Stryker Corporation. Again, they are “cups” designed to fit into the acetabulum in the pelvic bone. The Stryker Corp. is based in Michigan although these two components were made in their plant in Cork, Ireland. The FDA had previously (late 2007) sent a warning letter to Stryker about unsanitary conditions in its New Jersey plant.
Potential class action lawsuits
Many lawyers are planning and expecting class action suits to begin over the Trident recalls. If you have had a hip replacement, ask your doctor whether any Stryker components were used in your surgery.