As recipients of DePuy metal-on-metal hips continue to experience premature implant failure, metallosis, and other side effects, the medical device maker... read more
Defective Hip Replacement Parts
The artificial hip implant is designed to replace the components of the natural hip, usually damaged by arthritis. When a patient receives an artificial joint, the damaged natural joint is removed.
The hip is one of the body's true ball and socket joints. The patient's normal hip joint includes the acetabulum and femoral head. The acetabulum is the socket part of the joint; it is a cup-shaped indentation in the pelvis. The femoral head is the ball portion of the joint; it is a ball-shaped piece of bone that is an extension of the femur or thigh bone.
To replace the natural joint components, the surgeon places an artificial cup-shaped device into the pelvis, which becomes the artificial acetabulum. The artificial femoral head is a ball-shaped implant attached to a stem that is fit into a space made in the thigh bone by the surgeon.
The femoral head prosthesis connects to the stem by a neck. In some implants today, this lower part of the implant, that is, the femoral head, actually is made in three pieces: the head, the neck and the stem.
Different materials have been used for the artificial parts in an attempt to prolong the longevity of the prosthesis. Which materials are used depend upon the patient's age, physical condition, activity level and the preference of the surgeon.
Metal and Plastic Implants
A combination of metal and plastic have been the most commonly used materials for making the artificial joint. Both the acetabulum and femoral head are made of metal which can be:
- Cobalt chrome
A plastic piece is inserted as a spacer between the two parts of the joint. The metal parts are either press-fit into the patient's bone, in which case the natural bone grows around the implant, or are cemented in place with a special bone cement.
These implants wear out at a rate of about 0.1 millimeters per year. However, these implants can loosen over time, leading to local infection and possibly breakage of the implant as well as damage to the surrounding bone.
Metal-on-metal implants are similar to the metal and plastic implants, but no plastic spacer is inserted between the acetabulum and femoral head. These implants wear out about ten times more slowly than the metal-on-plastic implants, at a rate of about 0.01 millimeters per year. Even though the wear rate is slower, no data are available that show the implants actually last longer in the body.
A problem with the metal-on-metal implants is metal debris is cast off by the implants as the parts rub against each other. This debris can lead to local infection around the implant and metal ions being released throughout the body via the bloodstream. It is not known what danger these ions pose. The U.S. Food and Drug Administration (FDA) has requested safety tests by manufacturing companies that make metal-on-metal hip implants to determine the dangers of the metal-on-metal implants.
Ceramic-on-ceramic implants hold more promise for longevity than even the metal on metal implants, according to reports. Wear is such an important issue in hip implants because wear is related to loosening. When the implant loosens, revision surgery is necessary, which is painful and involves many other problems.
Ceramic implants are hard and smooth and long-lasting. However, no long-term data have been collected about the longevity of these implants because they are too new. In addition, there is the potential for "catastrophic failure" of the implant. This is less of a problem recently, but when this occurs the implant breaks within the body, requiring revision surgery.
Contact a defective hip attorney if you wish to seek compensation for a failed hip replacement.