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What’s the latest word in joint replacement?

By Jennie McKee

Panel reviews new technology, research directions

After receiving wrist implants, a young patient with severe rheumatoid arthritis has pain-free, flexible wrists for the first time in her life. A reverse total shoulder replacement enables an elderly patient with severe arthritis and rotator-cuff loss to lift his arm above his head and reach a can in his kitchen cabinet.

These technological innovations are the good news in orthopaedics according to a recent AAOS-sponsored Webinar attended by journalists from the consumer and trade press. Moderated by Frank B. Kelly, MD, the Webinar featured representatives from six orthopaedic specialty societies.

Advances in wrist replacement
According to Charles S. Day, MD, MBA, representing the American Society for Surgery of the Hand, wrist replacement may be an effective treatment for some patients.

Although wrist fusion is still the favored treatment, a study conducted by Dr. Day found that progressive loss of wrist motion creates incrementally significant functional limitations. Modifications to implant designs are making wrist prosthetics more effective and longer lasting.

“Newer implants are porous coated to encourage bone ingrowth and biologic fixation,” said Dr. Day. “They have excellent stability and enable better wrist motion compared to fusion. They can also last longer than previous generations of implants. Wrist implants are not for everyone, though; patient selection is key.”

Dr. Day noted that the future of wrist implants is bright.

“We can look forward to even more biologically active fixation—a ‘living glue’ that adheres the prosthesis to bone,” said Dr. Day. “The possibility of using wrist implants in younger patients exists. In addition, super strong, friction-free materials may be developed.”

The spectrum of shoulder replacement options
Joseph P. Iannotti, MD, PhD,
representing the American Shoulder and Elbow Surgeons, discussed a wide spectrum of treatment options for shoulder replacement.

“Options for shoulder replacement range from the most conservative (covering only the humeral head) to very complex replacement that’s performed for specific types of shoulder problems,” he said.

Dr. Iannotti noted that orthopaedic surgeons consider many factors—including patient age, activity level, amount of damage to the rotator cuff, and the amount of bone loss that may be present on the glenoid and humeral head sides—before deciding what type of arthroplasty to perform.

“Most traditional shoulder replacement patients can expect a very high functional outcome,” said Dr. Iannotti. “We tell our patients that 90 percent of them can expect implant longevity of 15 to 20 years, based on current materials.”

Some patients, however, are not good candidates for traditional shoulder replacement. For ex­ample, reverse total shoulder arthroplasty—which was approved by the Food and Drug Admin­istration (FDA) in 2004—may be the best option for elderly patients with severe arthritis and rotator cuff loss.

The role of computer navigation in TKA
“Why should an orthopaedist use computer navigation during total knee arthroplasty (TKA)?” asked Jay D. Mabrey, MD, of the American Association of Hip and Knee Surgeons. “Because computer navigation significantly improves the alignment of a total knee replacement.”

According to Dr. Mabrey, several reports have found that computer navigation is effective in aligning total knee implants. Researchers have also found that better aligned total knee replacements last longer.

Computer navigation devices consist of three major components: infrared sensors, a guidance screen, and a computer that controls the entire process. To determine the mechanical axis of the leg, the surgeon attaches sensors to the bone. The computer calculates the location of the sensors in three-dimensional space. Accurately aligning the cutting jigs with the mechanical axis enables precise placement of the new components.

Dr. Mabrey estimates that using computer navigation during TKA adds only 5 minutes to the length of the operation.

“When a surgeon uses computer navigation, he or she doesn’t have to put guide rods down into the thigh bone, so the patient doesn’t lose as much blood,” said Dr. Mabrey, who cited the example of a patient undergoing bilateral TKA. “We did both of the knees with no blood transfusions. In addition, we achieved near perfect alignment.”

Trends in ankle replacement
Keith L. Wapner, MD, representing the American Orthopaedic Foot and Ankle Society, said that several factors have made it more difficult to obtain success in total ankle arthroplasty than in TKA or total hip arthroplasty.

Because almost all cases of ankle arthritis develop after a trauma, said Dr.Wapner, “the soft tissue envelope is often compromised, as is the ankle joint itself.” In addition, the smaller surface of the ankle joint must absorb greater forces than other joints. These factors make survival of non­biologic materials in the ankle joint more difficult than in other joints. New prosthetic designs are made for bone ingrowth, rather than cement fixation.

“Newer designs and a better understanding of the forces on the implant have allowed us to develop replacements that we hope will be able to address and correct problems that stem from the biomechanics of the ankle,” said Dr. Wapner.

“Mobile-bearing implants basically consist of a metal component that covers the end of the tibia, a metal component that covers the talus, and then there’s a free piece of polyethylene that sits between those two metal pieces,” he explained. “In the fixed-bearing design, the polypropylene component is attached to the tibial tray.

“Ankle replacements hold the promise of pain relief as well as more normal ankle motion than can be provided by the traditional treatments of bracing and ankle fusion,” added Dr. Wapner. “Allowing our patients to have normal ankle motion should enable them to have a more normal lifestyle.”

The latest in cervical disk replacement
“Cervical disk replacement is one of the best examples of successful new technology in the world of surgical treatments for spinal disorders,” said Alan S. Hilibrand, MD, of the Cervical Spine Research Society.

According to Dr. Hilibrand, the results of an early FDA study comparing disk replacement with the traditional treatment—anterior cervical fusion—showed similar outcomes in terms of pain reduction over a 2-year period.

Early data have also suggested that disk replacement may lead to fewer re-operations. Another potential benefit is that disk arthroplasty may minimize or prevent adjacent segment disease.

“Approximately 25 percent of patients who undergo fusion develop a condition known as adjacent segment disease, which involves pinched nerve pain or spinal cord compression at an adjacent level,” said Dr. Hilibrand. Whether cervical disk replacement can minimize or prevent adjacent segment disease is still under study.

Dr. Hilibrand predicts that more devices will soon be approved by the FDA. He also noted that patients with two or three levels of arthritis and spinal cord compression are not good candidates for cervical disk replacement.

“Although these patients might initially feel better, they likely would soon develop new problems that would need treatment,” said Dr. Hilibrand.

The future of orthopaedic research
Joshua J. Jacobs, MD, past president of the Orthopaedic Research Society, noted that orthopaedic researchers continue to seek ways to predict and prevent osteolysis, which can lead to aseptic loosening of the implant. Researchers are examining whether biologic or genetic factors might govern the response to debris and lead to osteolysis.

“Recent research has found a certain gene form that is more commonly present in patients who develop osteolysis and loosening than in those who don’t,” said Dr. Jacobs. “This gene codes for tumor necrosis factor alpha, a potent cytokine, that is known to induce inflammation and actually cause bone loss.”

Osteolysis research could help orthopaedists provide patients with tailored, individual care based on their genetic makeup. “We need to develop large genetic databases on patients with total joint replacements, correlate how the implant performs with the type of genes they have, and then possibly select different types of implants for those who seem to have a genotype that may predispose them to failure,” explained

Dr. Jacobs. “We’re also working very hard on developing reliable preoperative screening tests to dictate material selection in patients undergoing total joint replacement surgery.”

Disclosure information for all of the Webinar participants can be found online at www.aaos.org/disclosure

Jennie McKee is a staff writer for AAOS Now. She can be reached at mckee@aaos.org

What else did they say?
The AAOS media Webinar “Hands, Shoulders, Knees and Toes . . . and Back: The Most Breaking News in the Joint” attracted the attention of journalists from media outlets such as The New York Times, The Wall Street Journal, Reuters, and the Associated Press. The Webinar is also available to AAOS members and the general public. Visit www.aaos.org/newsbureau and click on “Press Kit for Hands, Shoulders, Knees and Toes . . . and Back.”

AAOS Now
January 2009 Issue
http://www.aaos.org/news/aaosnow/jan09/clinical8.asp