March 24, 2006 -- A torn ACL in the knee can be replaced -- but it can't be healed. A new technique now shows promise to change this.
Doctors long ago gave up trying to repair a torn ACL (anterior cruciate ligament). That's because the important knee ligament, essential for running and jumping and keeping the knee stable, almost never heals right. A new technique may overcome the ACL's famous reluctance to heal.
The idea is to promote healing by building a kind of bridge to connect the two halves of a torn ACL. The bridge keeps fluids in the knee from washing away repair cells, says orthopaedic surgeon Martha M. Murray, MD, head of the sports medicine research lab at Children's Hospital in Boston.
"The repair cells are looking for a place to go and heal, but they get lost in the fluid," Murray says. "We developed a collagen bridge to give the cells a place to crawl into and be happy and functionally heal. With this bridge, the cells just go crazy. We found that to be incredibly exciting."
While the technique is exciting, it's still experimental. Murray's team is still experimenting in animals. Human tests are years away. Why? It's still not clear how well the healing works. If the ACL doesn't heal back to full strength, it could suddenly give way.
Lonnie Paulos, MD, professor of orthopaedic surgery and co-director of the sports medicine program at Baylor College of Medicine, Houston, applauds the researchers' effort.
"It is a good project," Paulos tells WebMD. "I just bet it is a long way off. If I were a betting man, I'd bet we don't see it in my lifetime."
Murray and colleagues report their findings in the April issue of the Journal of Orthopaedic Research.
Torn ACL: Current, Future Options
The ACL is the big ligament that keeps your knee stable as you run and jump. Athletes sometimes suffer a torn ACL. It's one of the worst sports injuries. That's because unlike other torn ligaments, the ACL won't completely heal.
"The ACL does heal. The problem is, it does not heal under the proper tension," Paulos says. "What was once a high-tension cable is now a piece of spaghetti."
Murray and Paulos note that doctors used to try to repair the ACL by stitching it back together. That didn't work very well. After a year or two, the ACL would rupture again.
So doctors gave up on trying to repair a torn ACL. Instead, they took it out and replaced it. Paulos says the first choice for replacement is tendon from another part of the patient's leg. The second choice is using tendon from a deceased organ donor.
Surgeons now have learned to do this operation using arthroscopic techniques, which require only small incisions. Even so, it's a big operation. About six months are needed for recovery.
Original ACL vs. Replacement ACL
Even when everything goes perfectly, the replaced ACL isn't as good as the old one, Murray and Paulos note. The original ACL has all kinds of muscle fibers that may rest or fire as the knee goes through its motions. Moreover, the original ACL is shot through with nerve fibers that tell other muscles to help. Replacement ACLs just don't do all these things.
And there's another problem.
"With ACL reconstruction, you are at increased risk of arthritis in that knee," Murray says. "If you do get arthritis -- well, there is not a good solution for patients in their mid-30s who already have knee arthritis. They are pretty young for a knee replacement, and we don't have a good way to make their knee cartilage come back."
Murray says her team is working hard to bring the new technique to humans. They're now working with pigs, whose knee anatomy is much like that of humans. But it will take time to know whether the healed ACLs in these animals are durable.
"Our patients are really important to us," Murray says. "It will be at least two or three years before we are confident enough this will work before we do this in people. If everything goes perfectly every step of the way, it could be before then. But the reality of research is we find something we have to fix. We would rather get this right than get this fast."