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Bioengineered ACL Could Help Injured Knees

In rabbits, researchers used animal's cells to help grow new ligament

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HealthDay Reporter

TUESDAY, Feb. 20, 2007 (HealthDay News) -- A new bioengineered anterior cruciate ligament (ACL) replacement could provide a new treatment option for the more than 200,000 Americans who rupture their ACLs annually, U.S. researchers report this week.

"We're hoping that we can have this as a solution for patients within the next three years," said study lead researcher Dr. Cato Laurencin, professor and chairman of orthopaedic surgery at the University of Virginia in Charlottesville.

Working with rabbits, his team used three-dimensional, braided polyester "scaffolds," that were sometimes (but not always) seeded with cells taken from the animal's ACL as a replacement for ligaments surgically removed from the animal's knee.

Both the cell-seeded and unseeded scaffolds worked well, Laurencin said, though the seeded scaffolds performed better. "Without cells, it takes longer [for the tissue to regenerate]," he said.

The study was published in this week's early online edition of the Proceedings of the National Academy of Sciences.

The ACL is one of four ligaments that connects the tibia (shinbone) to the femur (thigh bone). According to the American Academy of Orthopaedic Surgeons, the ligament may be injured in a variety of ways -- for instance, when landing after a jump or rapidly changing direction.

The typical treatment for a torn ACL, Laurencin said, involves surgical replacement using either a piece of the patient's own patellar or hamstring tendons, or material from a cadaver.

Using the new "biomimetic" scaffold, however, Laurencin's team was able to reconstitute and repopulate the tissue without the use of self- or cadaver tissues. "Histological studies showed we were able to obtain excellent in-growth of ligament-like tissue in the scaffold, and our mechanical studies demonstrated that we had a reasonably good retention of mechanical properties at 12 weeks, suggesting the ligament tissue being formed was having functional capabilities."

According to the study, the rabbits could begin to bear some weight on the repaired knee within just 24 hours after surgery.

Yet much work remains to be done before this scaffold can be used to treat human patients, said Dr. Diane Dahm of the Mayo Clinic College of Medicine in Rochester, Minn.

"I applaud the authors for their investigation," Dahm said. "The idea of using a bioresorbable scaffold to allow cell migration and, ultimately, replacement of native ACL tissue is interesting and potentially clinically relevant."

But, Dahm said, the bioengineered ligament has its limitations. "The high rate of rupture suggested that the scaffold underwent resorption and loss of strength before the replacement tissue was able to withstand biologic mechanical loads," she said. "When seeded with native ACL cells, the rupture rate was lower but still substantial."

Laurencin said his next step will be to test the scaffold in large animals such as sheep or goats, and that he is looking for corporate partners to help commercialize his invention.

But Dahm believes that "significant information" is still needed before human clinical trials can begin, including data on inflammatory responses to the scaffold, the rate of cellular infiltration, and how the mechanical properties of the scaffold change over time.

"Perhaps the use of growth factors to speed cell migration and collagen production will be required," she said. "Treatment of the [scaffold] to slow resorption, thus maintaining mechanical properties for a longer time period, might be required."

More information

For more on ACL, visit the American Academy of Orthopaedic Surgeons.

SOURCES: Cato Laurencin, M.D., Ph.D., Lillian T. Pratt Distinguished Professor and chairman of orthopaedic surgery, and professor of biomedical engineering and chemical engineering, University of Virginia, Charlottesville; Diane Dahm, M.D., assistant professor of orthopedics, Mayo Clinic College of Medicine, Rochester, Minn; Feb. 20-23, online edition, Proceedings of the National Academy of Sciences

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