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Why is it that a tear of the ACL typically requires surgical replacement

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The author has something of a conflict of, so most of this answer (shown in blue) will be cribbed from an article published in the AAOS newsletter.


It is, in a way, a paean to Martha Murray, who graduated from Penn Med in 1994 and is now a professor at a Harvard


"Suture repair of a torn ACL is generally unsuccessful—with a failure rate of 90 percent. As a result, the current standard treatment for an ACL tear is to remove the ligament and replace it with a tendon graft."


ARTIST'S IMPRESSION OF WHAT ACL REPAIR WOULD LOOK LIKE (The repair is surrounded by an envelope to keep the healing factors in place, an issue discussed below)

"Dr. Murray and her team designed a series of experiments to define key biologic differences in healing between ligaments such as the medial collateral ligament (MCL) that heal and those such as the ACL that don’t."

They first compared fibroblasts in the ACL with those in the MCL. They found that cells in both injured ligaments have comparable rates of proliferation, that each ligament was able to revascularize after rupture, and that collagen production in each ligament was comparable up to 1 year after injury. But in the injured MCL and other extra-articular ligaments, a provisional scaffold developed—something that was not seen in the ACL.

The synovial fluid that surrounds the ACL washed away the blood clot that forms as an early bridge between the two torn ends of the ligament. As a result, “there was no structure in place to rejoin the two ends of the ligament, no place for surrounding cells to invade and remodel into a functional scar tissue,” said Dr. Murray. The researchers hypothesized that the lack of a provisional scaffold between the two ends of the torn ACL was the key mechanism behind its failure to heal."





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