When the painkillers stop working, arthritic joint damage in the big toe can make even the weight of a bedsheet agonizing.

Standard surgery eliminates that pain by removing the cartilage and fusing the bones, but at the expense of mobility.

Cartiva Inc's implant - made of the same substance used in contact lenses, called hydrogel - was approved for big-toe surgeries by the U.S. Food and Drug Administration in July.

It is designed to mimic natural cartilage and can achieve the same pain relief as surgery while retaining joint-mobility.

"It's reasonable to expect this could end up becoming the largest procedure done on the foot and ankle in the United States," Chief Executive Tim Patrick said in an interview.

Nearly 50,000 surgeries on the big toe will be conducted in the United States this year, according to iData Research.

The condition, known as hallux rigidus, affects one in 45 Americans over the age of 50, or about 2 million people. As the U.S. population ages, these numbers are expected to grow.

Cartilage provides a smooth, gliding surface for joint motion and acts as a cushion between bones.

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In patients with osteoarthritis, which affects about 27 million Americans, the cartilage breaks down, causing pain and inflammation and limiting motion. Osteoarthritis can affect any joint, but occurs most often in knees, hips, hands and big toe.

Unlike bone and other connective tissue, cartilage has little or no ability to repair itself.

If drugs, braces, physical therapy, weight loss and activity restrictions don't work, the next step is usually surgery.

The most common procedure, called fusion, uses plates and/or screws to join the bones. That can limit activities such as playing sports or wearing high-heels, and requires a recovery period of up to twelve weeks.

Two years of data on Cartiva's implant, Cartiva SCI, showed that patients experienced a faster recovery compared with fusion patients and comparable pain relief.

Privately held Cartiva, a 20-employee company based in Alpharetta, Georgia, expects to capture about 40 percent of the U.S. market within five years, Patrick said.

DURABILITY QUESTIONED

While Cartiva's product has advantages, some experts wonder about its durability, noting that older implants made of silicone, plastic and metal have limited clinical evidence and tend to degrade over time often due to particulate accumulation.

"It's a good thing for prolonging a joint's use without doing something more drastic, like a total joint replacement ... but nobody knows how long this hydrogel will last," said Dr. Arthur Coury, a professor of chemical engineering at Northeastern University in Boston.

"There are some horror stories of hydrogels degrading in the body and what they have done, when they're meant to be long-lasting."

Data from a small study tracking Cartiva patients for five years after implantation showed that more than 90 percent of those evaluated retained normal or near-normal joint function.

"I think Cartiva's product needs to be validated over a much longer period of time before fusion is replaced to a major degree," Coury told Reuters.

The advantage of Cartiva's technology is that the patient can still opt for fusion if necessary.

In the study used to win FDA approval, the re-operation rate for Cartiva SCI patients was 12 percent, about the same as for those who underwent fusion.

Cartiva's implant is priced between $3,500 and $4,000.

A fusion of the big toe, excluding a metal implant, costs between $4,000 to $6,000, said James Laskaris, an emerging-technologies analyst with MD Buyline, which provides clinical and financial information to hospitals.

The price climbs to about $10,000 including the metal implant, Laskaris said.

Cartilage regeneration, which uses the patient's own cells and is typically used in the knee, costs between $20,000 and $30,000 and works best in younger patients, Laskaris said.

Cartiva's implant has been approved in Europe since 2002 for damage that involves both the cartilage and underlying bone. The company has since won similar approvals in Canada and Brazil.

The FDA, though, requires separate trials for each joint.

Cartiva SCI is currently being tested for a joint at the base of the thumb. The company is years away from testing it for hips, Patrick said.