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 been experiencing severe complications associated with their hip replacement.
Historically, the use of hip implants was limited to patients who had suffered hip fractures or who were older, less active and suffered from severe arthritic hip conditions. However, advances in hip replacement design, the materials they are made from and the surgical procedures used to implant them have made hip arthroplasty one of the most common orthopaedic procedures today. In fact, surgeons are now offering the procedure to patients younger than 55 — to correct a wide variety of hip conditions that previously would not have been considered severe enough to warrant the surgery.
As hip implants began to be used in a younger and more active population, they were pushed beyond their design limitations. To address the more active lifestyle, new implants from stronger materials have been developed to more closely mimic the natural motion of the hip joint. Although these new designs have made hip implants available to a wider array of patients, complications are more common and in some cases more severe.
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 complications. Some of the most important complications associated with these procedures are due to the materials the implant components are made of.
Particle Debris from Hip ImplantsIn total hip replacement and hip resurfacing, the new cup and the new ball (or ball covering) can lead to complications. As the implant recipient moves their legs, 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 debris primarily made of cobalt and titanium ions, which can cause a condition known as metallosis. 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.
MetallosisMetallosis 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. It is more often seen in hip resurfacing patients than in total hip replacement patients. Primarily this is due to two issues. First, most hip resurfacing implants are used in younger, more active recipients — who tend to place a higher level of wear and tear on the implant than older recipients. Second, hip resurfacing implants tend to have a larger femoral ball than total hip replacement implants. Because the femoral ball is larger, there tends to be more abrasive wear within the joint, which produces more metallic debris. However, metallosis can occur in metal-on-metal total hip replacements. This usually requires the failure of the articular interface, which is a plastic insert that separates the metal femoral component from the metal acetabular cup.
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. The full impact of metallosis is not fully known. However, it has been linked to several hip replacement complications, 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
OsteolysisOsteolysis, 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.
The body’s autoimmune reaction also releases cells called macrophages, which in turn release bone reabsorption stimulators. Since hip implants continuously release particle debris, the body’s autoimmune response is continuous as well. Since the bone in the area is only stimulated to reabsorb bone and not produce it, eventually, the bone around the implant will degrade to the point that the prosthesis will loosen and eventually fail.
Other Serious Hip Replacement ComplicationsAlthough 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 325,000 times a year in the United States, and is considered by many to be routine surgery, the associated complications can be very dangerous and even deadly.
MortalityA 2003 study published in the Iowa Orthopedic 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.
DislocationThe 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 postoperatively.
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 is most likely to occur within the first few months after surgery.
Heterotopic OssificationHeterotopic 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.
InfectionWith 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.