Joint Distraction Surgery: A New Option for Ankle and Knee OA
Repairing, not replacing, joints may be the next step in arthritis care.
Treatment for hips and knees worn down by arthritis is usually straightforward: joint replacement surgery. But surgical solutions for osteoarthritic ankles are less clear-cut. That's because most traditional methods relieve pain at the expense of long-term joint health. Joint repair through joint distraction arthroplasty may offer the best solution.
Traditional repair methods such as fusion – or arthrodesis – require bones in the ankle and leg to be permanently locked together with plates and screws. Pain relief can be dramatic, but it comes at a price: an abnormal gait, potential arthritis in nearby joints and an ankle too immobile for sports or climbing stairs.
The alternative is an artificial joint, similar to a hip or knee implant. Ankle replacement is more complicated though, and requires a high degree of surgical skill. Ankle implants also tend to wear out quickly, making them a poor choice for the younger, more-active patients who often need them.
"Most people with knee arthritis are in their 60s and thinking about retirement, whereas ankle arthritis frequently strikes people in their 40s who need to function and provide for their families," explains Gregory C. Berlet, MD, an orthopaedic surgeon at the Orthopaedic Foot and Ankle Center in Columbus, Ohio.
Some doctors advise younger patients to grin and bear it until a better option comes along.
But that option may already exist. Called joint distraction arthroplasty, it uses the body's natural repair mechanisms to heal the joint without damaging it.
Distraction involves pulling the joint surfaces slightly apart and holding the bones in place with pins set in an external fixation frame. The theory is that the absence of mechanical stress on the joint combined with changes in intraarticular fluid pressure allows damaged cartilage to repair itself, explains Austin T. Fragomen, MD, director of the Limb Lengthening Clinic at Hospital for Special Surgery (HSS) in New York City and assistant professor of orthopaedic surgery at Weill Cornell Medical College.
HSS physicians have used distraction arthroplasty for ankle arthritis for a decade and recently began using it for knees.
The procedure itself is relatively straightforward. Surgeons remove any bone spurs – growths common in ankle arthritis – and drill small holes in the bone (called microfracture) to help stimulate cartilage repair.
"These are standard procedures we've been doing for dozens of years with mediocre results," Dr. Fragomen says. "What is exciting is adding distraction to it."
The next step is assembling the frame, which is composed of one or more rings, about six inches in diameter, that encircle the ankle like a halo. Pulling the rings apart and locking them stretches the joint surfaces about 5 millimeters – less than a quarter inch.
Mesenchymal stem cells from the patient's bone marrow are used to jumpstart the repair process. Because they can transform into cartilage cells, stem cells are often used in orthopaedic surgeries.
"We're constantly tweaking the way we use stem cells," Dr. Fragomen says. "We have the option of just injecting them into the ankle, putting them into a fibrin matrix, which is like sticking them in jello, or we can mix them with small pieces of [donor] cartilage in hopes that will help form an even better layer of new cartilage."
Patients wear the fixation frame, which Dr. Fragomen admits is bulky and apt to "tear the sheets," for about three months then switch to a temporary walking boot. Full recovery takes close to a year.
By then, a thin layer of new cartilage has formed, bone swelling is reduced and subchondral cysts – fluid-filled sacs that are common in osteoarthritis – have been absorbed.
Dr. Fragomen says, "What we see subjectively is improvement in function and a dramatic decrease in pain. The goal is for patients to be able to get out of bed and walk and stand for prolonged periods – to walk the dog or go hiking. And in 75 percent of cases, they can. That the procedure has a 75 percent success rate is supported by five different studies."
It's not known why distraction fails in about a quarter of treated patients. "Some of it is biology; the bone simply doesn’t respond," Dr. Fragomen notes.
It's also not clear who is best suited for the procedure.
"Distraction arthroplasty was developed for young people, but I've had patients over 60 who wanted to try it," Dr. Fragomen says. "And we found that older patients actually scored highest on functional measures. So we try not to exclude too many people who could benefit."
Anyone with a functional range of motion is a candidate, including patients with post-traumatic arthritis, which develops years after a fracture or other injury. Distraction is not an option for people who lack all ankle motion or have advanced inflammatory arthritis.
The most common complication is an easily treated infection at one of the pin sites. Severe pain, Dr. Fragomen says, is rare.
The benefits of distraction athroplasty last at least 10 years – the amount of time HSS has followed patients. If symptoms recur, the process can be repeated. Or, if ankle implants continue to improve, replacement surgery may eventually become a satisfactory option for younger patients.
One small 2011 study published in Annals of the Rheumatic Diseases, suggests distraction is as good for arthritic knees as it is for ankles. According to lead investigator Floris Lafeber, a professor of experimental rheumatology at the University Medical Center Utrecht in the Netherlands, 25 patients undergoing knee distraction saw a significant improvement in pain and function.
"Patients start at 80 percent of the maximum pain score, which is severe pain, and it decreases to about 20 percent. Functional ability improves to 80 or 90 percent," he says.
Dr. Fragomen speculates that knee distraction hasn't caught on because knee replacement surgery is familiar, works well and requires less time and patience than distraction procedures. Still, he forsees the day when restoration therapies will repair cartilage at an early stage, avoiding joint replacement altogether.
"Our cartilage regeneration techniques aren't effective enough at this point," he says, "but this is just the beginning."