Whether Kevin Durant’s calf strain can be healed through non-operative interventions will be seen through his jump shot. (Kevin N. Hume/S.F. Examiner)

Breaking down calf strains

Until recently, it was believed most injured muscles couldn’t be fully restored

Calf strains are in the air. No, not different kinds of baby cows: but the strained muscle kind that sidelines great basketball players — like Kevin Durant. Here is what is known and new about them.

The calf muscles are primarily the two heads of the gastrocnemius and the deeper soleus muscle. They connect to the foot through the Achilles tendon. Strains of the muscle are code words for tearing. When it is just the muscle that tears, the treatments do not involve surgery. When the tendon tears, most commonly we repair it with a percutaneous (through the skin) tendon repair. Open surgery is rarely required.

Calf muscle strains (i.e., tears of varying degrees) are defined by muscle fiber separation. They usually occur after landing awkwardly from a jump or a sudden push off in a sprint—actions where the muscle contraction is more forceful than the individual fibers can withstand. Small amounts of fiber disruption are called mild sprains. The more fibers disrupted, the more severe the label: moderate, severe, or complete rupture. In top athletes trying to hide the severity of their injury, the “strain” label is often used when, in fact, there is a complete tear of the muscle—or even worse, of the tendon attached to it.

Muscle injuries, unlike tendon or ligament ruptures, are typically followed by profuse bleeding, inflammation, remodeling, and regeneration. Muscles have an abundant blood supply, so that when the fibers tear there is an immediate rush of blood to the site of injury—and with the blood, comes stem and reparative cells. While one might think this would lead to rapid healing, the fact is that, the repair cells directing such healing are inhibited by unique cells, which lay down scar tissue rather than normal muscle fibers. The healing of the muscle is initially somewhat disordered, and only over time (with exercise and hormonal stimulation) can it be remodeled. The exercise induces hypertrophy (enlargement) of the muscle fibers while the hormones, with their specialized growth factors, direct individual fiber regeneration.

Until recently it was believed that most injured muscles could not be fully restored to normal. This misconception has been overturned by encouraging studies of heart muscles: after the heart’s blood supply is temporarily interrupted (which is called myocardial infarction), injured heart muscles have been restored with a direct injection of stem cells.

Inflammation itself was also thought to be a bad thing. Athletes consumed buckets of anti-inflammatory drugs after both minor and major muscle strains. Our current understanding of the muscle repair sequence, however, shows that inflammation is a necessary part of healing: It recruits the key stem cells that direct muscle fiber regeneration. This has inspired novel ideas about how to work with inflammation. The cells and growth factors recruited in this phase of injury and repair can be augmented by additional growth factors and specialized cells from bone marrow, fat, or amniotic tissues injected into the injury site to shorten the entire healing cycle.

So the calf strain is really a “mini-model” of every injury and of most repair processes. And the treatment is evolving. We are moving beyond rest, ice, and anti-inflammatories to a more active protocol that includes controlled exercise to induce remodeling; alternating ice and heat to improve blood flow; and injections of tissue-specific growth factors which, as they recruit muscle-specific progenitor and stem cells to the site of injury may induce rapid and normal tissue regeneration.

As long as a calf strain is really a strain—rather than a complete tear of the muscle and tendon requiring surgical repair—non-operative interventions can cure the injury. Only the athlete, agent, surgeon, and MRI know for sure. In Kevin Durant’s case, the proof will be in the jumping.

Dr. Kevin R. Stone is an orthopedic surgeon at The Stone Clinic and chairman of the Stone Research Foundation in San Francisco.

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