Among the most dreaded of injuries feared by athletes at all levels is tearing the anterior cruciate ligament, commonly known as the ACL tear. Yet University researchers are now beginning to understand the reasons for the difficult rehabilitation process.

Up until now, researchers and practitioners alike have been baffled by the muscle’s inability to completely regain its strength after an ACL tear, even following surgery and rehabilitation. But new research could be a crucial development in the path to understanding how to fully restore the muscle.

ACL injuries are seen most commonly in sports which require pivoting of the leg, such as soccer, basketball and lacrosse, among others. Any time a foot is planted and an athlete is changing directions, there is a high likelihood that the knee joint can give out and tear the ligament. Bedi said that ACL patients typically undergo surgery and physical therapy treatments to restore the tear and avoid damage that could lead to arthritis.

The research — conducted by a clinician-scientist team comprised of Dr. Asheesh Bedi, M.D., assistant professor of orthopaedic surgery, sports medicine and shoulder surgery and Dr. Chris Mendias, Ph.D., A.T.C, assistant professor of orthopaedic surgery and molecular & integrative physiology at the University’s Medical School — have found a new drug target that may prevent muscle atrophy, which is the weakening and loss of muscle tissue, and is frequently associated with ACL damage.

Myostatin is a hormone that blocks muscle growth and appears to work at elevated levels after muscle tears, according to a previous study cited in the University of Michigan Health Systems press release.

After finding that myostatin surges after ACL surgical repair, Bedi and Mendias were led to believe that rest and rehabilitation after ACL surgery may not be enough to fully repair the damaged ligament.

Bedi said that muscle strength deficit is an ongoing problem for patients healing from ACL tears.

“Even if I do a perfect surgery and (patients) do a perfect job of healing, there is an inherent loss of muscle strength that occurs any time the knee is injured and certainly any time the knee is operated on,” Bedi said.

The study, which followed 18 patients suffering from ACL injuries — including several University student-athletes — tracked levels of myostatin after surgery to understand how they change and how they vary in respect to muscle damage.

“There’s been work trying to develop inhibitors for myostatin for patients with different muscle wasting, such as muscle dystrophy,” Mendias said, “But we’re the first to look at myostatin levels in this population of physically active individuals with ACL injuries.”

MedSport physical therapist Daryl Montie said recovery times vary from individual to individual.

“Ideally I get the opportunity to see patients in the interim between injury and surgery with goals of reducing swelling, inflammation and pain, and restoring normal range of motion,” Montie said. “Post-operative rehabilitation is quite different for each patient depending on a variety of factors.”

However, even with the 4-to 8-month healing and therapy process, the muscle weakness associated with ACL tears can still translate into impaired play or increased risk of re-injury, Bedi said.

Despite a successful surgery, even in the setting of a perfectly healed ACL, athletes suffer weakness in quadriceps and hamstrings that may turn into a barrier on their ability to return to competition or play. This has led researchers to believe that in addition to surgery and therapy, there may be a third hurdle of recovery of muscle strength.

“Where this research is novel is the thought that perhaps there are biological factors, myostatin being one of them, that are elevated, and elevated levels of those molecules are responsible for the inability for the muscle to fully strengthen,” Bedi said. “If there were ways that we as doctors can modulate that activity, then perhaps we can help to shift the balance in the favor of the athlete to regain that muscle mass.”

Female athletes in sports involving jumping are particularly susceptible to ACL tears because of their knock-knee landing pattern, Mendias said. In terms of prevention, there has been a push for athletes at all levels to focus on landing techniques to prevent ACL damage.

This research of this biological response component to ACL tears is paving the way for full recovery of muscle atrophy that may give injured athletes the opportunity to return to their level of elite play.

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