MMA Injuries: Why doesn't the ACL heal on its own?

Joe Camporeale-US PRESSWIRE

UFC flyweight John Dodson suffered a partial tear of the ACL last December, narrowly dodging the dreaded ACL reconstruction bullet. Here is a look at the science of why this ligament can't heal on its own when torn completely.

Knee injuries, and anterior cruciate ligament (ACL) tears in particular, are an all-too-common occurrence in MMA. It seems we hear of another MMA athlete suffering a torn ACL on a near weekly basis. The typical course of treatment includes surgical reconstruction of the ACL, followed by rehab lasting 8-12 months. Seldom does a fighter suffer an ACL injury that doesn't require surgery. However, that is just what happened to UFC flyweight John Dodson at the end of 2013.

In December of last year, Dodson was forced out of his scheduled bout against Scott Jorgensen at UFC on FOX 9 due to a knee injury. Initial reports pointed toward a serious knee injury. However, on December 5, Dodson posted a video on Twitter indicating that he had partially torn his ACL and medial collateral ligament (MCL), and expected to be out 8-10 weeks. Now, Dodson has recovered to the point that his next fight has been scheduled- June 7 vs John Moraga in Albuquerque, NM.

Dodson's partial ACL tear offers us the chance to examine why the ACL cannot heal when it is completely torn. The MCL is considered an extra-articular ligament, meaning that it lies outside of the knee joint. The ACL is an intra-articular ligament. Unlike the ACL, the MCL heals quite well with a period of rest, possibly a brief period of bracing, and a rehab program to rebuild and maintain muscle strength. When the MCL is torn, a blood clot will form at the wound site. The clot serves as a provisional scaffold upon which the body will build a "bridge" of new collagen tissue that ultimately fills in the tear, thus healing the ligament. This blood clot formation does not occur when the ACL is torn. Since the ACL is located within the knee joint, it is exposed to a continual flow of synovial fluid. When the ACL is torn, the flow of synovial fluid prevents formation of the clot. The blood is dispersed within the knee joint, and the scaffold does not form. The lack of a scaffold also deprives the torn ligament of important proteins and other blood-borne substances needed for proper healing.

The fact that Dodson's ACL wasn't completely torn is important. The intact portion of his ligament, with its intact blood flow, in essence served as the scaffold. This allows for healing of the ligament with new collagen tissue.

Dodson has probably gone through a battery of tests as part of his rehabilitation, in order to ensure that there is no clinical evidence of abnormal laxity of the ACL. Abnormal clinical testing, even in light of a partial vs complete ACL tear, would have probably meant surgery for Dodson.

Dodson is set to fight John Moraga in a flyweight bout at UFC Fight Night 43 on June 7.


Klapour, AM, Murray, MM. Basic science of anterior cruciate ligament injury and repair. Bone Joint Res 2014;3:20-31.

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