When metal hips are used in hip replacement surgery, patients can suffer from bone death, dislocation, infection, metallosis, implant failure and other serious complications. Total hip replacement, partial hip replacement and hip resurfacing have unique risks.
Hip replacement surgery (hip arthroplasty) has been touted by many experts as one of the most significant medical device innovations of the last 40 years. It has helped millions of people overcome painful arthritis, recover from hip fractures and improve their quality of life. However, hip implants do not come without risk or complications. A growing number of implant recipients have experienced implant failure and other severe hip replacement complications.
There are three types of hip replacement surgery. With total hip replacement, the entire hip joint — ball and socket, as well as femoral stem — is replaced. Partial hip replacement requires only the ball (femoral head) to be replaced. In a hip resurfacing procedure, the cup is replaced, but the ball is not. Instead, the ball is reshaped and covered with a metal cap.
Each procedure accomplishes its goal in a slightly different fashion, but they share some of the same potential for hip replacement problems.
What are Common Hip Replacement Complications?
Hip replacement surgery comes with risk of complications such as:
- Blood clots
- Differing leg lenghts
- Device loosening
In some patients, a small amount of pain or instability can occur after surgery. There may also be some stiffness and bleeding as well as blood vessel or nerve injury.
Many patients experience relief from hip pain caused by osteoarthritis and can increase mobility following surgery. But, like other surgeries, hip replacement carries its own set of risks and complications that require immediate medical attention or even additional surgeries to treat.
The type of implant may also increase the risk for certain complications. For example, studies show metal-on-metal implants have greater risk of loosening or early failure because metal particles released from the device may weaken nearby bone and tissue. Popular brands of MoM implants include the DePuy ASR and Pinnacle, Smith & Nephew Emperion and Birmingham Hip and the Biomet M2a-Magnum.
Total Hip Replacement and Hip Resurfacing Risks
In total hip replacement and hip resurfacing, particle debris from the cup and ball (or ball covering) can lead to complications and implant failure. As the implant recipient moves, the surfaces of these two components rub against each other. The friction and abrasive wear between these two components cause debris to be produced. It is estimated that every step taken with a hip implant produces between 100,000 and 1 million particulates of debris.
The type of debris produced depends on the material the components of the implants are made of. Different materials can cause different long-term complications. For example, hip implants known as metal-on-metal hips — where both the femoral component and the cup are made of metal — will create metal debris, also called ions which can cause a condition known as metallosis. Device makers make implants out of several metals — primarily cobalt, chromium, titanium, nickel and molybdenum.
On the other hand, hip implants known as metal-on-plastic — made of a metal femoral component and a plastic cup — create polyethylene particles that can lead to a condition known as osteolysis.
Metallosis is a rare condition that is caused by the buildup of metallic debris in the soft tissue of the body — in this case the soft tissue surrounding the hip joint. Metal debris from metal-on-metal hip implants can cause grey discoloration of the tissue surrounding the implant, usually indicating that the tissue is oxygen-starved and dying. The effects of metallosis can be particularly acute in implant recipients who have a condition known as metal sensitivity. In patients who have metal sensitivity, metallosis can lead to metal poisoning.
Cobalt, chromium and titanium ions, in particular, are linked to several toxic reactions in the body. Cobalt and chromium make up the surface area of many implants and studies link them to cellular toxicity, allergic reactions, cancer and inflammation. and surrounding tissues. Scientists have less research data on titanium ions, but device makers typically do not use this metal as a surface coating on bearings. Instead, titanium corrodes over time and releases ions. Some evidence links these ions to destroying bone and impairing cell function.
The full impact of metallosis is not fully known. However, it has been linked to several hip replacement side effects, including:
- Severe joint pain
- Implant failure
- Implant loosening
- Local tissue necrosis (tissue around the implant dies)
- Deterioration of the bone around the implant
- Formation of cysts or pseudotumors
If metal ions spread from the surrounding tissues into the blood and blood ion levels become too elevated, it can cause a host of other physical conditions such as mental cognitive problems, emotional imbalance, severe headaches and problems with the nervous system.
Osteolysis, or periprosthetic osteolysis, is the loss of bone around the hip replacement. It is the body’s attempt to clean up particle debris, plastic or metal, produced by the implant. Osteolysis is the most common long-term hip replacement complication. It has also been named as the cause of nearly 75 percent of all hip implant failures.
Osteolysis occurs when the body recognizes the implant debris as foreign and reacts to remove the particles. The body releases enzymes, cytokines and other cellular reactions into the area, all in an attempt to either expel or dissolve the particulates, which causes a chronic inflammatory condition.
Risks Associated with Partial Hip Replacement
Risks associated with partial hip replacements include dislocation, infection, loosening of the implant and post-operative pain. During the procedure, the femur may be fractured.
In a partial hip replacement (hemiarthroplasty), the femoral head (the ball) of the hip only is replaced. The socket is left alone. Replacing the femoral head becomes necessary when the ball exhibits severe damage from arthritis, degeneration or fracture. Another instance where partial hip replacement may be appropriate is when a broken hip occurs at the femoral neck.
Partial hip replacement may be more stable than total hip replacement, and the surgical procedure is less complicated. However, recovery results of these surgeries are inconsistent. These surgeries present a unique danger because the artificial metal ball touches the natural cartilage in the hip socket. This can cause the cartilage and surrounding tissues to become weak and less healthy, causing more problems over time. With a total hip replacement, the socket is replaced.
People suffering from conditions such as bone cyst in a local area, thin bone in the socket or other facture may be more appropriate candidates for total hip replacement surgery. Once the femoral head is arthritic, total hip replacement is required.
More Hip Replacement Risks & Implant Failure
Although metallosis and osteolysis are two of the more dangerous complications associated with hip implants, there are other serious complications to be aware of. Although hip arthroplasty is performed more than 450,000 times a year in the United States, and is considered by many to be routine surgery, the risk of associated complications can be very dangerous and even deadly.
A 2003 study published in the Iowa Orthopaedic Journal reviewed the results of nearly 5,000 hip arthroplasty surgeries. It found that the mortality rate for patients having the surgery for the first time was nearly 1 percent. For patients undergoing a revision surgery, the mortality rate skyrocketed to 2.5 percent. Researchers also found that the most important determining factor of mortality was age. Patients older than 70 were three times more likely to die from the surgery than younger patients.
The natural hip is held in place by a ligament that connects the ball to the socket. It is also held in place by thick, dense tissue that surrounds the joint. During hip replacement surgery, this tissue is removed and dislocation can occur. Proper placement of the implant during surgery is vital to it remaining in place for the long term.
Although dislocation is not very common, it occurs following 1 percent to 5 percent of initial surgeries. Following revision surgery, the risk for dislocation rises as high as 20 percent. Dislocation leading to implant failure is most likely to occur within the first few months after surgery.
Heterotopic ossification is the process of bone forming outside of the skeleton, meaning soft tissue is calcified. Typically, it occurs in areas of the body where severe trauma has occurred. In the case of hip arthroplasty, the muscles around the hip joint calcify and become stiff.
Heterotopic ossification is considered one of the most common hip replacement complications, occurring in nearly 50 percent of patients. However, only about 10 percent of those suffer any side effects from the condition, including tenderness, swelling and a decreased range of motion. The condition can be treated with low-dose radiation and anti-inflammatory drugs. In severe cases, surgery is required to remove the calcified tissue.
With an incidence rate of about 1 percent, infections following hip surgery are not common. If the infection is caught within four weeks after surgery, doctors may re-open the wound to clean it and inject antibiotics. If that does not work or if the infection is not discovered until later, the implant may need to be removed and later re-implanted after the infection has been eradicated. To avoid scar tissue and bone degeneration, re-implantation needs to occur within three months.
Infection is one of the most feared postoperative complications. In the most extreme cases, where the infection cannot be controlled, the entire hip and leg may have to be amputated. It is exceptionally rare for a patient to have to undergo a transpelvectomy, or hip-disarticulation — in which the entire leg, including the hip joint, are removed and replaced with a prosthetic limb.
Avascular Necrosis (Osteonecrosis)
Avascular necrosis is bone death caused by lack of blood and can lead to implant failure. It is more often associated with hip resurfacing than total hip replacement. With hip resurfacing, the metal cap that covers the femoral ball can reduce the amount of blood reaching the ball. If the bone is deprived of blood for an extended period of time, it will collapse, which will destroy the bone and use of the joint will be lost. In extreme cases, the implant will have to be replaced. Since the femoral ball is no longer usable, a total hip replacement is required.
Implant components can loosen over time, which is considered the most serious long-term complication because it is the strongest indicator that a revision surgery will be required. A component could loosen because it is worn out or because the cement fails to hold it in place. However, loosening of a hip implant could also point to a more serious condition like osteolysis or metallosis. If loosening is suspected, doctors will use a series of X-rays, taken over a period of time, to detect movement in the components and to determine if any corrective actions are necessary.
Periprosthetic fractures are bone breaks that occur around the implant and could cause the implant to fail. These fractures typically occur because the bone around the implant has been weakened by osteoporosis, medications, pressure from the implant or stress placed on the implant. Periprosthetic fractures occur around hip implants following a little more than 1 percent of first surgeries and 4 percent of revision surgeries.