What Is a Hip Replacement?
The hip, a ball-and-socket joint, is one of the largest weight-bearing joints in your body. The socket (acetabular component) is formed from the pelvis bone, and the ball (femoral component) sits at the top of the femur.
Arthritis and joint injury, such as hip fracture, can cause severe pain and limitations, which make it difficult to perform usual activities. A hip replacement is a surgical procedure that replaces the damaged hip joint with an artifical hip prosthesis. The surgery is usually performed when other treatments fail to relieve pain and when limitations greatly interfere with daily routines.
What Is a Metal-on-Metal Hip?
There are several different types of hip prostheses available. Your doctor will choose the one that is right for you after considering your body structure and activity level. The goal of hip replacement surgery is to relieve pain, restore range of motion, and improve joint function.
While all hip prostheses have two components, the ball and socket, they can be made of different material. Over the years, manufacturers of hip prostheses have attempted to make them more durable, so that they will last many years before a revision (repeat) hip surgery is needed. Generally, the ball is made of a strong metal or ceramic material. The socket, often referred to as the cup, can be made of plastic/polyethylene, metal, or ceramic. With a metal-on-metal hip, as the name suggests, both the ball and socket are made of metal. Metal-on-metal hips are used for total hip replacement surgery, as well as hip resurfacing procedures.
Metal-on-Metal Hips: The Expectation
When metal-on-metal hips first became available, expectations were high. They were expected to be more durable and last longer than older polyethylene/metal prostheses. Polyethylene/metal hips had known complications associated with wear. As the metal ball rubs against the polyethylene lining of the cup, the polyethylene can flake off and small particles can cause osteolysis (where the immune system attacks surrounding bone), and ultimately loosening of the prosthesis.
Developers thought that metal-on-metal hips would circumvent the problem of debris and prosthesis loosening. Also, because metal-on-metal hips are larger, it was thought that it would be a more stable artificial joint and less likely to dislocate. Suffice to say, metal-on-metal hips were developed in order to minimize complications associated with older prostheses. But, as it turns out, metal-on-metal hips are not problem-free.
Metal-on-Metal Hips: The Problem
It has been found that metal-on-metal hips also shed debris as they wear. They also can corrode. Metal ions and particles can be found in the space around the prosthesis and in the bloodstream. When this occurs, you can experience increased pain and swelling around the hip, osteolysis, and symptoms in other parts of your body.
Do not be misled, though, by sensational news reports and television ads from lawyers promoting lawsuits. Most people with metal-on-metal hip implants have not developed problems. Still, the U.S. Food and Drug Administration (FDA) is being vigilant about the potential problems. In February 2011, the FDA released a public health communication regarding metal-on-metal hips. In May 2011, the FDA ordered postmarket surveillance studies of metal-on-metal hips.
Higher Risk Patients for Complications With Metal-on-Metal Hips
All types of hip implants have benefits and risks. At this time, only a couple of specific models of metal-on-metal hips have been recalled. The use of metal-on-metal hips for many patients is still considered favorable. Certain people, though, are considered unsuitable candidates for metal-on-metal hips, including those:
- with known allergies to metal
- with known kidney problems
- with a suppressed immune system
- taking high doses of steroid medication, such as prednisone
- women of child-bearing age
The Bottom Line
Problems with metal-on-metal hips are considered rare. If you are not sure which type of hip implant you have, ask your orthopedic surgeon. If you experience pain around the hip prosthesis, increased pain while walking, swelling, or any changes that concern you, contact your doctor.
6/30/2012 UPDATE: FDA Advisory Committee Sees Little Reason to Use Metal-on-Metal Hips
Questions and Answers About Metal-on-Metal Hip Implants. American Academy of Orthopedic Surgeons. September 2011.
Metal-on-Metal Hip Implant Systems. FDA. 3/29/12