A therapy that aims to heal injured body tissue with targeted sound waves may bring pain relief to people with chronically injured hamstring tendons, a small study of professional athletes suggests.

The treatment, known as shockwave therapy, delivers pulses of sound waves to areas of injured body tissue, via a hand-held probe placed on the skin.

Shockwaves have also been studied, with mixed results, as an alternative treatment for a range of orthopedic and sports-related injuries, when more conservative therapies fail. Those include heel pain caused by a condition called plantar fasciitis, as well as tennis elbow, Achilles tendon injuries, stress fractures and “frozen” shoulder.

In the U.S., shockwave devices are approved for treating plantar fasciitis and tennis elbow. The therapy is more widely used in Europe, where it was developed.

In the new study, reported in the American Journal of Sports Medicine, Italian researchers tested the effectiveness of shockwave therapy against chronic cases of so-called proximal hamstring tendinopathy (PHT) in 40 professional athletes.

The injury affects the tendons connecting the hamstring muscles (at the back of the thigh) to the “sitting bones” of the pelvis. It typically causes pain at the top of the hamstring that radiates to the back of the knee, especially during physical activity or while sitting. In an MRI scan, the tendon is also visibly thickened.

As with other types of tendon injuries, PHT can often improve with conservative measures like rest, anti-inflammatory painkillers and physical therapy. Whether shockwave therapy is useful for stubborn cases of PHT has not been clear.

All of the athletes in the current study had had recurrent pain and tenderness from PHT for at least six months. Researchers led by Dr. Angelo Cacchio, of the University of Rome, randomly assigned the patients to either four sessions of shockwave therapy over four weeks or a standard regimen of conservative therapy - consisting of rest, pain medication, physical therapy and strengthening and stretching exercises.

Three months after starting treatment, patients receiving shockwaves reported a greater improvement in pain symptoms, on average, than those on conservative therapy. Seventeen of 20 shockwave-therapy patients reported at least a 50-percent reduction in pain, versus only two of 20 in the comparison group.

Athletes in the shockwave group also reported fewer limits on their activity than their counterparts on conservative therapy.

The findings, Cacchio told Reuters Health in an e-mail, indicate that low-energy shockwave therapy can be safe and effective for chronic PHT. However, he said, larger studies are still needed to confirm these initial results.

The study included only pro athletes - soccer and rugby players, distance runners and track and field athletes - but chronic PHT can affect the recreational athlete as well.

Whether shockwave therapy might be appropriate for the weekend warrior would depend on a number of factors - if, that is, the therapy is even available to him or her.

Cacchio pointed out that, in general, shockwave therapy is used as a last resort to avoid surgery, after rest, pain medication and physical therapy fail. Some people - including those who have medical conditions or are taking medications that increase their odds of internal bleeding - should not have shockwave therapy. And the therapy’s safety for children, pregnant women and people with nerve damage from conditions such as diabetes is not yet established, Cacchio said.

In this study, there were no serious complications. But Cacchio noted that “misdirected” treatment can actually damage tissue; receiving the therapy from an experienced doctor is important.

More common and minor potential side effects include temporary swelling, pain and skin irritation at the site of the treatment.

No one is completely sure how shockwave therapy works against orthopedic injuries. A leading theory is that “microtrauma” to the treated tissue boosts blood flow to the area, promoting natural tissue repair.

In Italy, four sessions of shockwave therapy cost about the equivalent of $200, according to Cacchio. In the U.S., prices vary and insurers may not cover the cost.

SOURCE:  American Journal of Sports Medicine, online September 20, 2010.