November/December 2013

Rising Demand for Total
Hip Arthroplasty

By Carolyn Gutierrez
Today’s Geriatric Medicine
Vol. 6 No. 6 P. 30

Advances in hip replacement surgery have allowed thousands to maintain an active lifestyle. In 2007, The Lancet termed total hip replacement surgery, which is performed each year on approximately 285,000 arthritis sufferers in the United States, “the operation of the century.” With several varying techniques, total hip arthroplasty (THA) has become a pain reliever for many but also has stirred some controversy thanks to a recent implant recall.

Causes of Joint Deterioration
“The most common reason to need hip replacement is osteoarthritis, the wear and tear of the joint,” says Scott Ball, MD, an associate clinical professor and the chief of adult joint reconstruction at the University of California, San Diego School of Medicine. Also known as degenerative joint disease, osteoarthritis is localized in weight-bearing joints such as the hip and knee. As joint-cushioning cartilage wears down over time, severe pain and stiffness result. It occurs most often in people over the age of 50.

Other types of arthritis can hasten the need for hip replacement. Rheumatoid arthritis, the most common type of inflammatory arthritis, is an autoimmune disease in which the synovial membrane is chronically inflamed and thickened, leading to cartilage damage and persistent pain. Posttraumatic arthritis, resulting from a hip fracture or injury, and avascular necrosis, in which the surface of the bone underlying the cartilage of the femoral head collapses because of a lack of blood, also cause disabling hip pain that may be relieved by THA.

Nonsurgical options such as anti-inflammatory medications, physical therapy, walking supports, and cortisone injections typically are the first line of treatment. Once these treatments have been exhausted, THA can be considered. The decision to undergo surgery is a highly individual one contingent on quality-of-life concerns. If persistent hip pain and immobility prevent a patient from engaging in work and recreational activities and affect his or her sleep, THA may provide a solution.

According to literature from the American Academy of Orthopaedic Surgeons, there are no age or weight restrictions on patients who elect to undergo THA. Although the average age of a hip replacement patient is 60, recommendations for the procedure are based on levels of pain and disability.

Ball says potential problems following THA include dislocation (an approximate 1% risk), infection (0.5% risk), and blood vessel or nerve injury (0.5% risk), complications that usually require revision surgery. Other rare surgical risks include instability, aseptic loosening of the implant, a femur fracture (either shortly after surgery or years later), and leg length inequality. Generally speaking, these risks have declined dramatically over the past 50 years as THA technology has improved and surgical protocols have been established.

Surgical Approaches
The posterior approach is a commonly used surgical technique for THA in which the hip is accessed through a large curved incision centered over the buttock. This approach, which is thought to provide better visualization of the hip, involves splitting muscle tissue. Another popular route, the anterolateral approach, involves a straight incision over the side of the hip and requires less cutting of muscle tissue than the posterior technique.

The minimally invasive direct anterior approach, in which the surgeon makes one or two small incisions over the front of the upper thigh, currently is receiving much attention. Although there is less muscle disruption with this approach, visualization of the hip joint is limited, making it a more technically challenging procedure.

Ongoing controversy exists within the orthopedic medical community as to which surgical method is the most beneficial. To date, studies have failed to find significant postoperative differences in dislocation rates and other complications or distinct advantages among any of the various approaches to THA. “Ultimately, the difference is where you are going to see your scar three months after surgery: the front or back of the body,” Ball says.

The advantages associated with any approach are defined by the method in which a surgeon is most adept. Ball recommends that patients seek a surgeon who performs at least 50 THA procedures per year, preferably in a hospital where about 500 of the surgeries are done annually. “The hospital experience really matters as well,” he says. “You want the patient to go to a relatively high-volume surgeon who works in a relatively high-volume hospital to ensure that they have good nursing care, therapy, and follow-up.”

Implants
Traditional THA involves removing the arthritic ball-and-socket hip joint and replacing it with biocompatible components made from metal-on-polyethylene, metal-on-metal, ceramic-on-ceramic, or various hybrid systems incorporating elements of all three. The implant generally is composed of three sections: the stem fitting into the top end of the femur; the ball, which acts as a replacement for the femoral head; and a cuplike hollow socket to replace the acetabulum, the cavity of the pelvis holding the joint in place.

The implant components either are cemented into place using an acrylic polymer or “press fit” into the bone, a process in which new bone growth actually attaches to a special surface coating of the implant. A combination of cemented and cementless components also is commonly used.

For patients wanting to avoid a traditional total hip replacement, hip resurfacing may present an option. In this procedure, although the acetabulum is replaced, the top end of the femur is not removed, and the femoral head is encased with component material.

Implants made of metal-on-polyethylene have been the most commonly used and are considered to be safe and durable. More than 90% of metal-on-polyethylene implants last 10 years. The primary disadvantage is the possibility that the polyethylene, a high-performance plastic resin, will shed debris over time, possibly leading to osteolysis, an autoimmune response to the debris in which there is dissolution of the bone and aseptic loosening of the implant.

Ceramic-on-ceramic implants are considered beneficial because of their hard surfaces, high wear resistance, low friction, and fewer debris particles. However, ceramic-on-ceramic implants are expensive and require high levels of proficiency when implanting. Also, early dislocation is possible if the insertion is not exact. In addition to these potential drawbacks, these implants have been known to produce a disconcerting squeaking sound in the hip.

Metal-on-Metal Implant Complications
According to Jeffrey Lozman, MD, an orthopedic surgeon at Capital Region Orthopaedics in Albany, New York, use of the metal-on-metal technique has steadily increased over the past 15 years until recently. Ball concurs, noting that “there are studies that show between 2005 and 2006, more than one-third of hip replacements in America were done with metal against metal.”

Concerned about debris from polyethylene components, surgeons have revisited the metal option with the belief that modern technologies have improved the alloys and the problematic designs that compromised them in the 1970s. Because metal is less brittle than polyethylene, scientists could formulate a larger and stronger femoral ball, creating enhanced stability and, in theory, decreasing the risk of dislocation.

All hip implants, regardless of their construction, shed varying amounts of debris over the short and long term. Despite remarkable durability, wear and corrosion on the metal-on-metal bearing surface results in elusive microscopic debris, or nanoparticles, that release metal ions such as cobalt and chromium that can enter the bloodstream. Over time, concentrations of these metal ions may cause inflammation in the joint as well as pain, tissue damage, and implant loosening. Eventually, revision surgery to replace the implant may be necessary.

A 2008 study of patients who had undergone metal-on-metal hip resurfacing uncovered several cases of pseudotumors. Although it was a small finding—1% after five years—it is troubling because these tumors ultimately can compromise muscle and bone.

In 2010, DePuy Orthopaedics recalled Articular Surface Replacement (ASR) hip resurfacings and ASR XL total hip replacements after the UK Medicines and Healthcare Regulatory Products Agency issued safety alerts for ASR and all metal-on-metal implants. Two joint registries from Australia and the United Kingdom also had reported high failure rates for the ASR devices and all large-diameter metal-on-metal total hip replacements.

“What happened was that [studies] found an increased incidence of metal-on-metal wear and metal debris in and around the hip joint in an increasing percentage of patients,” Lozman says. “Now that we are keenly aware that this is occurring, we’re looking for it, and we’re seeing it more often than we intended on seeing it when [the implants] became popular over a decade ago.”

Experts believe that a design flaw in the hip “cup” has made the ASR components prone to what orthopedic surgeons call “runaway wear,” in which the implant’s normal wearing process is accelerated, resulting in even higher concentrations of metal ions.

The ASR systems were used in more than 93,000 patients worldwide, with approximately one-third of them in the United States. It was estimated that 40% would experience implant failure within five years. Perhaps as a result of the findings, the use of metal-on-metal hip components has decreased dramatically in the last two years.

The FDA recommends that patients with metal-on-metal implants who have no discernable symptoms follow up with their orthopedic surgeons every one to two years for monitoring. Patients experiencing pain or any other adverse reactions are advised to have physical examinations, X-rays, and blood tests to measure metal ion concentration. In some cases, MRI and ultrasound may be recommended.

“It’s extremely unfortunate, this whole thing with the ASR, because a lot of patients have been hurt by it,” says Ball, a specialist in metal-related implant research who routinely performs revision surgery. “Fortunately, the ASR represents a very small percentage of hip replacements that have been performed. [Nevertheless], I feel like it’s overshadowed the benefits of a hip replacement a little bit.”

— Carolyn Gutierrez is a freelance writer in New York City.