It started with research that just wasn’t working.
Chelsea Bahney, a Ph.D. student studying tissue engineering, was trying to regrow cartilage in damaged knees and other overused joints. The problem was that the cartilage tended to do what it was designed to do: turn to bone. And cartilage that turns to bone is no good at cushioning joints.
But the frustrations of one researcher can sometimes be the boon of another. In Bahney’s case, a colleague at UCSF pointed out that cartilage that turns to bone might just be good for something else: growing new bones.
“It was an obvious idea that people hadn’t really explored yet,” said Bahney, now a postdoctoral researcher at UCSF. “We had this cartilage that we were trying to engineer for joints, but it was becoming bone.”
It’s a decision that would be of special interest to orthopedic surgeons who tackle the toughest bone injuries. Bone grafting is a common and often successful procedure for replacing bone tissue lost to injury or disease. It involves scraping bone tissue from another part of the body – usually from the patient’s hip, but sometimes from cadavers – and transplanting it to the area where the damage was done.
Limitations of grafts
When the graft is successful, it spurs new bone growth to replace the bone that was lost. But if there’s a large chunk of bone missing – for example, in a soldier who’s lost part of his leg in combat, or a child who’s had a tumor carved out of her arm – a graft might not produce enough new bone, or there could be complications like infections that inhibit growth. These patients often have multiple surgeries, and the failure rate can be as high as 50 percent, depending on the type of injury.
“We’re better than we used to be at it,” said Dr. Theodore Miclau, chief of orthopedics at San Francisco General Hospital. “But there’s still a variety of patients who have problems that are so difficult that they might need multiple operations or sometimes even an amputation.”
An amputation is what Eric Navarro was facing in December, more than a year after he broke both bones in his lower leg while chasing a suspect as a San Jose police officer. Navarro jumped over a fence and landed badly, resulting in a compound fracture – his tibia broke through the skin of his leg.
Since his injury in June 2010, Navarro has had multiple surgeries, including one to put three plates and “30-something” screws into his leg. A bone graft failed, and he was referred to doctors at San Francisco General.
“I was ready to just cut it off,” Navarro said. Instead, doctors fused the bones in his lower leg and ankle; he’ll find out Wednesday if the surgery was successful.
Navarro’s case is exactly why Miclau said he’s intrigued by the work his colleagues at UCSF are doing. What’s unusual about the UCSF research is that the scientists aren’t studying techniques for improving bone grafting, they’re looking at ways to replace bone grafts with cartilage transplants.
Benefits of cartilage
In some ways, using cartilage instead of bone is a “no-brainer,” said Ralph Marcucio, a researcher in orthopedic surgery who is working with Bahney.
Cartilage is a stiff but flexible tissue that connects some bones and offers support and cushioning in the joints and other places where bones come together. In human development, cartilage makes up the first skeleton in developing fetuses, before being replaced by bone.
It’s that process, of shifting from cartilage to bone, that scientists are looking at as a possible alternative to bone grafting.
“The entire skeleton is a cartilage template that turns to bone,” Marcucio said. “These (cartilage) cells want to make bone.”
The research being developed by Bahney and Marcucio is still very new and has only been tested in mice. The scientists released results from their first study last month at the Orthopaedic Research Society’s annual meeting in San Francisco.
They found that when cartilage from one mouse is transplanted into the site of a bone injury into a second mouse, the cartilage does indeed promote new bone growth.
Such a procedure wouldn’t work in humans, mostly because humans don’t have enough spare cartilage for a transplant. Unlike bone, cartilage doesn’t regenerate, and most adults’ supply of cartilage diminishes with age.
Turning to stem cells
But scientists have been able to grow cartilage in a lab using stem cells, and it’s possible that cartilage could be used in a transplant. That will be the next study for Bahney and Marcucio: to test how effective stem-cell-derived cartilage is in spurring bone growth in mice.
Still, it’s possible the stem-cell-derived cartilage won’t work, Marcucio said. And if it does, it may not be safe for use in humans.
“We haven’t tested the quality of healing,” meaning, it’s far too early to say whether growing new bone from cartilage is an improvement over bone grafting, Marcucio said. “The translation of our work into people is going to be tricky.”
Erin Allday is a San Francisco Chronicle staff writer. firstname.lastname@example.org
This article appeared on page A – 1 of the San Francisco Chronicle