Doctors are testing new ways to spur cartilage to regrow in damaged knees, from implanted “cartilage plugs” to injections of bone-marrow stem cells.
The need is huge. Knees are the joint most likely to go bad, and the cartilage that cushions them has only a limited natural ability to repair itself.
The question is how to unlock that ability and give it a boost.
The potential new options are being tried first in people who injured their knees and thus need small amounts of cartilage to regrow. But if they truly work, the techniques one day might offer hope for arthritis sufferers, too, whose cartilage over time completely erodes.
Most eagerly anticipated: the first clinical trial using stem cells from donated bone marrow to try to regenerate the knee’s shock absorber, a cartilage pad called the meniscus.
Meniscus injuries are common, and not just among young athletes. Because the pad weakens with age, a simple wrong step can leave an older person with the painful tear. About 800,000 Americans a year have part of the meniscus surgically removed, to relieve pain when jagged edges won’t heal.
Stem cells are building blocks for tissue. Mesenchymal stem cells are a type of adult stem cell that live in the bone marrow and can transform into cartilage-forming cells called chondrocytes. Mixing these stem cells with a knee-lubricating fluid helped the meniscus regrow in goats. Will it work in people?
Researchers enrolled 55 patients who had about half their meniscus removed. About a week after that surgery, each participant received a single injection — either a dummy shot or one containing millions of mesenchymal stem cells.
With a high-powered MRI machine, scientists now are measuring each patient’s remaining meniscus, for signs of regrowth.
“No one’s ever looked at the meniscus in terms of volume,” says Dr. C. Thomas Vangsness Jr. of the University of Southern California, lead researcher for the study funded by stem cell producer Osiris Therapeutics. “It’s very interesting what I’m seeing.”
While he reports no safety problems, he can’t say yet if the stem cells are working because the study still is blinded, meaning researchers don’t yet know which patients got the real injections. Initial results are due in October.
“It’s very, very exciting research,” says Dr. David C. Johnson, an orthopedic surgeon and sports medicine specialist at Washington Hospital Center in the nation’s capital, who is closely watching the work.
But, “it’s like The Sorcerer’s Apprentice,” he cautions. “You want to make some cartilage cells. Well, how do you turn it off? You don’t want too many. ... We’re sort of walking a tightrope.”
The meniscus isn’t the knee’s only cartilage. A tougher kind called articular cartilage coats the ends of bones so that they glide past each other smoothly instead of grinding — and if stem cells can regrow the meniscus, trying it on this cartilage is the logical next step, Johnson says.
Articular cartilage is the kind that wears away in arthritis, making total knee replacements the only option once a patient’s pain becomes too bad. Doctors have few surgical options for injuries to this cartilage, either, mostly trying a procedure that essentially roughs up the bone to stimulate natural repair.
The Food and Drug Administration initially approved the TruFit plugs as a filler for gaps in bone, not cartilage. But the plugs, officially known as bone-graft substitutes, have an almost magnetic ability to attract chondrocytes, explains Dr. Preston Wolin, sports medicine chief at the Neurologic and Orthopedic Institute of Chicago.
First, doctors started transplanting some of the patient’s own cartilage from a less stressed part of the knee into the harder-working injured spot, and using the plug to heal the weaker donor site.
That is “really robbing one part of the knee to pay the other part,” says Wolin. So now he and a number of surgeons use the plugs to fill the direct injury.
Washington’s Johnson is skeptical that the plugs produce cartilage as sturdy as the original.
But Wolin says he’s getting good results, with healing in a few months — faster than some other cartilage-repair surgery.
“This is not a substitute for knee replacement,” he cautions, because the plugs are only for small injuries, not arthritis’ widespread cartilage loss.
Manufacturer Smith & Nephew, which just bought the plugs’ original maker, is funding early stage research to see if the plugs could be expanded to cover a larger surface.