Platelet-enriched collagen gel may stimulate ACL repair

Growth-factor-rich gel regenerates knee ligament with 40% increase in strength.

A blood platelet-enriched collagen gel can stimulate natural healing of a partial ACL tear by encouraging the cells to fill the defect and restore mechanical strength to the ligament, according to a study in the Journal of Orthopaedic Research.

“This is a first important step in showing that the ACL can heal if we give it the right conditions,” Martha Murray, MD, lead author of the study, said in a press release announcing the study results. “That’s an important shift from thinking that the ACL has to be completely replaced after an injury.”

Using an animal model, Murray and colleagues at Children’s Hospital Boston evaluated the effects of a collagen gel mixed with platelet-rich blood plasma inserted into a partial ACL tear. They found that the gel provided a physical “bridge” between the torn ligament ends, while the platelets produced a variety of growth factors. Knees that received the gel showed greater defect filling at six weeks (43%) compared to untreated knees (23%).

Gel-treated defects also had a 40% increase in mechanical strength at six weeks compared with just 14% for untreated defects, according to the release.

Examining torn ACLs at the microscopic level, Murray and colleagues found that the ligament tries valiantly to heal itself. Cells migrate to the wound, growth factors are secreted and blood vessels grow to nourish the new tissue, but the ligament ends never join because there is nothing present to bridge the gap.

In most torn ligaments, a blood clot forms and acts as a temporary scaffold. Cells migrate onto this scaffold and begin fusing the ligament ends together. But in ACL injuries, fluid inside the knee joint dissolves the clot, preventing such scaffold formation.

After trying various materials, the researchers found that the collagen hydrogel mixed with platelet-rich blood plasma was firm enough to be used as a bridge and is not readily dissolved by joint fluid.

Murray cautions that the results are preliminary and more work is needed. But she hopes to eventually extend the ACL regeneration technique to humans using platelets from their own blood plasma, creating a less invasive ACL repair that would accelerate recovery and restore more normal knee function.

The research is being funded by the National Institutes of Health, the National Football League, the Orthopedic Research and Education Foundation and the Center for Minimally Invasive Technology. Murray is also developing an arthroscopic approach for inserting the gel and investigating ways to enhance the gel to speed healing.

For more information:
Murray MM, Spindler KP, Devin C, et al. Use of a collagen-platelet rich plasma scaffold to stimulate healing of a central defect in the canine ACL. J Orthop Res. 2006;24:820-830.