Research Summary: Healing ACL Tears

May 31 -- Nearly 100,000 Americans undergo ACL knee surgery each year. These torn ligaments are notoriously slow to heal. Now, innovative new research in animals may soon help people back on their feet in no time.

BACKGROUND: Anterior cruciate ligament (ACL) tears are knee injuries that afflict 100,000 Americans each year -- particularly teenage girls who are active. These tears are difficult to repair. Blood gets dispersed, preventing a clot from forming, and the two ligament ends don't fully reconnect -- there are still microscopic gaps. ACLs are reconstructed by replacing the torn ligament with a tendon graft, which works better than sewing the tear, but it isn't perfect. It's painful and doesn't result in full healing. Patients can go back to their normal lives afterward, but the actual mechanics of the knee is not fully restored, and arthritis may creep up later in life.

NEW TECHNIQUE: Martha Murray, M.D., an orthopedic surgeon at Children's Hospital Boston, and her team are experimenting with a new technique in animals. They're finding a collagen gel, enriched with blood platelets, can stimulate natural healing of a partial ACL tear, encouraging the body's cells to fill in the defect and restore mechanical strength to the ligament. The gel creates a physical "bridge" between the two ligaments ends, providing something for the cells to crawl back into and heal. Dr. Murray explains, "Even though ACL cells are happy to participate in the repair process, there's no place for them to do it. Our big finding was recognizing that the cells are fine -- they just need a bridge that they like." After trying various materials, her team found that the collagen hydrogel, mixed with platelet-rich blood plasma, was firm enough to be used as a bridge and wasn't readily dissolved by joint fluid.

RESULTS: So far, the technique has worked in 75 percent of animals tested. Although it will be years before researchers test it in people, Dr. Murray is very hopeful. She thinks it might not predispose patients to early arthritis, as it would make the knee more "normal" than grafting does. It is much less invasive, just requiring two incisions instead of taking out the patella and tibia to make a graft.

FUTURE: In the future, Murray hopes to extend her technique to other injuries like meniscus and rotator-cuff tears. Her ultimate dream is cartilage regeneration to repair joints damaged by osteoarthritis. No one has yet been able to repair cartilage, but Dr. Murray has discovered that even in bad osteoarthritis, cartilage has active, proliferating cells. She hopes to find another scaffolding material that would coat the pitted surface of damaged cartilage and recreate a smooth, nearly friction-free surface -- like filling in potholes in a road.