how muscles heal

Monday, July 27, 2015

This weekend, a friend self diagnosed a hamstring tear after feeling a pop and developing searing pain in the back of his leg, while sprinting at a family picnic. He joined Dustin Pedroia of the Boston Red Sox, who was placed on the disabled list this weekend with the same injury. It’s a reminder that weekend warriors and elite athletes share the same potential for pushing their bodies to the point of self-harm. The bad news is that the hamstring muscle group takes forever to heal and one cannot rush Mother Nature.

The hamstring is really a group of three muscles, the semimembranosus, the semitendinosus and the bicep femoris, that is responsible for flexing the knee. The muscles and their tendons attach to bones in the pelvis and then span the knee to attach into the tibia. When the muscles contract, the knee flexes; as well, they have another job to provide dynamic stability to the knee as it extends, when the quadriceps muscle on the front of the leg contracts. The two muscle groups need to be in balance, so that one group does not overpower the other.

Hamstring injuries occur when the muscle is aggressively stretched while running or jumping; it is usually not a contact injury. The injury is technically a strain and can occur within the muscle belly, within the tendon, at the junction where muscle turns into tendon or the damage can occur where the tendon or muscle attaches to bone and part of the one is avulsed or torn away. Grade one strains mean that the muscle fibers are stretched and not torn. Grad two strains mean that there is a partial tear of the muscle and grade three equals a complete tear.

Hamstring injuries take forever to heal…not quite literally forever, but often the time frame is measured by months and not days or weeks. The clinical healing is pretty straightforward, with pain and range of motion guiding how much the patient is allowed to do. It’s the stuff that happens at the cellular level that can help explain why rehab takes so long.

When a muscle tears, the injury and repair mechanism kicks into high gear. There are three phases of muscle repair. Initially, there is an inflammatory phase that last a few days, where the body sends in its scavenger cells that clean up the dead muscle fibers. These white blood cells (including leukocytes, monocytes and macrophages) are also responsible for sending chemical signals to activate growth factors that regenerate the broken muscle fibers. This begins the repair phase that will take 3-4 weeks to complete. The ruptured ends of the muscle begin to fuse by having scaffolding built by connective tissue that can bridge the gap and allow scar to form. This scar will hold the muscle together for the remodeling phase, where new muscle fibers and cells invade the scar tissue and ultimately replace it with functioning muscle. It takes 3 to 6 months. The healing process can sometimes derails and deposit excess scar tissue. This can limit the range of motion of the muscle and in turn make it weaker and more prone to injury. No matter how much the brain is willing to participate in rehabilitation, the cells can only work so fast.

Predicting how long it takes to return to play is an inexact science. A few studies have tried to help with the guesstimate. One group of athletes, who were able to walk without pain within a day, were able to return to play more quickly; otherwise, it was a minimum of three weeks away from their sport. Another study found that if significant pain were present for three days after injury, the recovery time would last more than 6 weeks. And finally, athletes who did not completely tear their hamstring and were able to retain their flexibility could expect to return to play within five weeks; unless they had had a previous hamstring injury and then their prognosis was not as good.

Elite athletes measure the length of their career, and more than a few weeks off can mean a season lost. A too early return to play can lead to potential recurrent injury, because the muscle remains weak and/or flexibility has not returned to normal. If the injury was caused because of poor biomechanics, the risk of another injury remains because the underlying condition was not addressed.

There is a balance in physical therapy and rehabilitation. Moving an injured muscle early on, promotes muscle fibers to regenerate and speed healing, but too much activity can lead to a larger scar and the risk of re-tearing the not quite healed muscle. Not enough activity will cause the muscle to atrophy or waste away, and perhaps be replaced with too much. This delays the ability to rehabilitate the muscle and restore strength. It is the art of the physical therapist that helps find the Goldilocks pace of rehab… not too fast, not too slow, but just the right speed.

As it turns out, my friend who was injured in his backyard, and Dustin Pedroia, injured at Fenway, will heal at the same rate so long as they listen to their body. The only difference? My friend will go to work and think of physical therapy in passing. Mr. Pedroia will go to work each day and there will think of nothing but physical therapy and getting his leg ready to return the basepaths.

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