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This guest column is by , an orthopedic surgeon and sports medicine specialist in Charleston, S.C. He writes about sports medicine on his and on .

One of the most challenging injuries suffered not only by competitive athletes but also active adults is a hamstring injury. It can cause people to miss weeks from their favorite sport or exercise. It can also put them at risk for suffering a repeat hamstring injury in the future.

Most treatment options for a hamstring injury within the muscle belly are nonoperative. Rest from the sport or exercise while the injury heals is critical. Other common treatments include anti-inflammatory medications, ice, compression, and even limited weight-bearing with crutches. Still, orthopedic surgeons have few options at our disposal to speed the healing of hamstring injuries.

Maybe it's the slow and unpredictable nature of hamstring injury healing that has stirred interest in the use of platelet-rich plasma (PRP) for these common athletic injuries. PRP is a fairly new treatment in which the physician draws a small amount of blood from the patient, spins it in a centrifuge to remove red blood cells, and re-injects the plasma concentrated with platelets. The platelets theoretically improve the body's healing response by delivering cytokines and growth factors into the injury site.

Unfortunately, recent studies have shown mixed results with PRP treatments for lateral epicondylitis (tennis elbow), Achilles tendinopathy, and osteoarthritis of the knee.

Addressing the Hamstring

A new study published in the October 2014 issue of the examined the effectiveness of single PRP injections for acute hamstring injuries.

, a sports medicine specialist, and colleagues at the University of Malaya Medical Center in Malaysia conducted a randomized, controlled trial with 24 athletes treated within 7 days of hamstring injury.

All athletes in the study were determined by ultrasound to have suffered partial tears (less than 33%) of the hamstring muscle fibers. Patient who randomized into the treatment group received a single injection of 3 mL of PRP delivered directly into the injury site by ultrasound guidance. Patients in both the treatment and control groups underwent progressive agility and trunk stabilization rehabilitation exercises.

The authors measured the effectiveness of PRP using one key outcome: return to play.

Specifically, patients had to be free of pain to direct palpation and pain-free with hamstring contraction. They had to show symmetrical range of motion compared with the opposite limb. They also had to demonstrate strength within 10% of the uninvolved limb on isokinetic testing. Then patients could resume full activities and increase training until reaching their pre-injury level of play.

Patients who received PRP for an acute hamstring injury did return to play faster. The mean time for return to play in the PRP group was 26.7 days, compared to 42.5 days in the control group. Likewise, half of the patients in the PRP group reached a point of full recovery by 26 weeks follow-up compared with 39 weeks for half of the control patients to do so.

"To the best of our knowledge, this is the first [randomized, controlled trial] to assess the effectiveness of a PRP injection for hamstring injuries," the authors concluded. "Our results showed that patients with a grade 2a hamstring injury treated with a single autologous PRP injection combined with [progressive agility and trunk stabilization] rehabilitation recover significantly earlier than controls."

Cautious Optimism

While I have been skeptical of the effectiveness of PRP for many musculoskeletal injuries, I am encouraged by these results for a difficult sports medicine injury. And it's good to see that the authors did not decide return to play simply by some gut instinct of the orthopedic surgeon or physical therapist that the patient could handle sports again. They used pain assessment scores and objective findings on isokinetic tests.

It is important to note that the patients were not blinded to the treatment. It would be hard -- and possibly unethical -- to draw blood from a patient in the control group if he or she would not receive the PRP treatment. It does raise the possibility that patients who received PRP might believe that they would do better and possibly would work harder in rehab to return to sports as fast as possible.

Finally, this study looks mainly at short-term return to play. It does not follow the patients for a longer period to determine rates of re-injury. We know that an athlete who suffers a hamstring injury is far more likely to suffer another hamstring injury than someone who has never suffered one. It is unclear from this study whether PRP would have any benefit in decreasing the risk of recurrent injury.

The study does at least give orthopedic surgeons and sports medicine physicians hope to treat athletes with hamstring injuries more effectively and help them return to sports more quickly and safely.

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