Hip joint deterioration can lead to pain, stiffness or difficulty walking. When these symptoms do not respond to conservative treatment, such as physical therapy, patients may be advised to undergo total hip replacement or hip resurfacing.
As part of this treatment, they may receive a "metal-on-metal" hip implant in which the "ball and socket" of the device are both made from metal. This webpage provides information on: hip implants, how metal-on-metal implants differ from other hip implants. The information provided on this webpage is not meant to replace a discussion with your health care provider.
During the June 2012 Orthopaedic and Rehabilitation Devices Advisory Panel meeting, the FDA reviewed available data and discussed the safety risks and effectiveness of metal-on-metal hip implants with patients, physicians, researchers, international regulatory agencies, professional societies, and manufacturers. Issues discussed included:
The Hip Joint
- Failure rates and modes;
- Metal ion testing;
- Imaging methods;
- Local and systemic complications;
- Patient risk factors; and
- Considerations for follow-up after surgery.
The hip joint is a ball-and-socket joint. The ball portion of the hip joint (femoral head) fits into the socket (acetabulum) of the hip bone (pelvis). The bone of the femoral head and acetabulum of the pelvis are separated by spongy material (cartilage) and by a sac of fluid (synovial fluid), both of which serve to lubricate the joint. A properly functioning hip joint is critical for normal everyday activities such as walking, running and climbing.
The cartilage or bones that make up the hip joint can deteriorate for a variety of reasons, leading to pain, stiffness or difficulty walking.
Painful hip conditions can be treated in several ways including physical therapy, exercise and medications. When a patient's symptoms do not respond to these treatments, an orthopedic surgeon may recommend traditional hip replacement surgery or hip resurfacing surgery.
Hip implants are medical devices intended to restore mobility and relieve pain usually associated with arthritis and other hip diseases or injuries. Every hip implant has a distinct set of benefits and risks. The key design features of each implant including size, material and dimensions make each system unique. In addition, the same hip implant system will have different outcomes in different patients. It is also important to recognize that hip implants may need to be replaced eventually. Factors that influence the longevity of the device include the patient's age, sex, weight, diagnosis, activity level, conditions of the surgery, and the type of implant chosen.
In the United States, there are currently five types of total hip replacement devices available with different bearing surfaces.
- Metal-on-Polyethylene: The ball is made of metal and the socket is made of plastic (polyethylene) or has a plastic lining.
- Ceramic-on-Polyethylene: The ball is made of ceramic and the socket is made of plastic (polyethylene) or has a plastic lining.
- Metal-on-Metal: The ball and socket are both made of metal.
- Ceramic-on-Ceramic: The ball is made of ceramic and the socket has a ceramic lining.
- Ceramic-on-Metal: The ball is made of ceramic and the socket has a metal lining.
An orthopedic surgeon should determine which hip implant will offer the most benefit and least risk for each patient. When making a recommendation, orthopedic surgeons should consider several factors such as the patient's age, weight, height, activity level, and cause of hip pain. Hip surgery may involve total hip replacement or it may involve hip resurfacing.
During total hip replacement
surgery, the damaged portions of the hip joint are removed. The ball (femoral head) is removed and replaced with a prosthetic ball made of metal or ceramic, and the socket (acetabulum) is removed and replaced with a prosthetic cup. The cup consists of one or two components made of metal, ceramic or plastic. A stem is also placed in the femur to support the femoral head. The femoral head attaches to the taper of the stem.
Hip surgery, like any medical procedure, carries risks. The risks of surgery include:
- A reaction to the anesthesia
- Heart attack
- Wound infection
- Excessive bleeding
- Blood clots
There may be adverse events after surgery, regardless of the type of hip system implanted including:
- Hip dislocation, when the ball of the thighbone (femur) slips out of its socket in the hip bone (pelvis)
- Bone fracture
- Joint infection
- Local nerve damage with numbness/weakness
- Device loosening or breakage
- Difference in leg lengths
- Bone loss
Patients who have hip implants should be aware of potential symptoms that may occur after 3 or more months after surgery that may indicate that their device is not functioning properly. Symptoms may include:
- Pain in the groin, hip or leg
- Swelling at or near the hip joint
- A limp or change in walking ability
- Noise (popping, grinding, clicking or squeaking) from the hip joint
Depending on the severity of the adverse event(s), additional surgery may be necessary.
Many of the recommendations, warnings and contraindications outlined here are from the manufacturers' labeling and the FDA website.
Metal-on-Metal Hip Implant Systems
Metal-on-Metal (MoM) hip implants consist of a ball, stem and shell, all made of metal materials. MoM hip implants were designed to offer the following benefits:
- Less device material wear is generated when the ball and socket rub against each other in comparison to other hip implants
- Decreased chance of dislocation when the ball of the thighbone (femur) slips out of its socket in the hip bone (pelvis)
- Decreased chance of device fracture
There are two types of MoM hip implants:
Traditional Metal-on-Metal Total Hip Replacement Systems
- Traditional total hip replacement systems
- Resurfacing hip systems
Metal-on-metal total hip replacement systems consist of a metal ball (femoral head), a metal femoral stem in the thighbone, and a metal cup in the hip bone (acetabular component). The ball attaches to the taper of the stem.
The FDA evaluates total metal-on-metal hip systems through its 510(k) program. Each system has multiple compatible components that must be identified. As of Nov. 30, 2012, the FDA had cleared 190 submissions for metal-on-metal total hip replacement systems, the majority of which were for modifications to previously cleared components. At this time there are five manufacturers of metal-on-metal total hip replacement systems in the U.S.
Source: FDA Website: http://www.fda.gov/medicaldevices/productsandmedicalprocedures/implantsandprosthetics/metalonmetalhipimplants/default.htm
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