Extracorporeal Shock Wave Therapy (ESWT) is something that has been around for a while but it seems to be having a renaissance. ESWT has been proven as an effective and safe non- invasive treatment option for tendon and other pathologies of the musculoskeletal system. I many times get the questions from patients as to what effect the “electric shock wave” will have on the body? We must realize that extra corporeal shock wave therapy has nothing to do with electricity. There is nothing mystical or cryptic about a shockwave therapy. It is nothing more than a sonic boom or sound wave. When a shockwave enters tissue, it may break up and reflect the absorption of kinetic energy by the precise body structures (bone, fat, tendon, ligaments), which are exposed to the shockwave. All techniques of shockwave production (electrohydraulic, electromagnetic and piezoelectric) depend on the conversion of electrical energy to mechanical energy. When a sound wave is transmitted into tissue, there are two levels of transmission: low energy and high energy. Low energy has an analgesic effect by either disrupting the cell membranes partially or completely. When high energy (any energy greater than 0.28mJ/mm2) comes in contact with the damaged tissue, there is a direct biological interaction. The following diagram gives us a better idea of what we speculate some of the mechanisms of action of ESWT might be.
I will discuss these aspects later in the article.
In recent years much research has been done in Europe and other portions of the world. ESWT continues to take on increasing importance in the stem cell field. The reason for this are many faceted. For instance, there are many different aspects of ESWT has on various stem cells, their environment, and their ultimate destination. As an orthopedic surgeon, I used this therapy a number of years ago for both tennis elbow and heel spur syndromes. Not only did I use it but I had good results with it. It fell out of favor due to the fact that it was not reimbursed by the insurance industry.
A few years ago, I became aware of ESWT again for its use in sports medicine and musculoskeletal problems. I think we are now understanding better the true mechanisms of how this is working. When I was lecturing in Brazil some time ago I met one of the worlds experts on shock wave therapy, a professor from a university in Munich Germany. We had quite a good discussion concerning the use of shock wave therapy in stem cell and PRP therapy. At that meeting, I had an epiphany when I realized that years ago when I used this technique I was actually creating an environment very conducive to stem cells. I go back to one of the basic concepts in Regenerative Medicine: “Cells not Doctors Heal Patients”. There were some surprising facts concerning the of the shock wave machines. They create a momentarily pressure that would be equivalent to an ocean depth of approximately 2000 ft. Luckily this pressure only lasts a fleeting moment. Under most conditions this would cause immediate destruction of the tissue and probably death. The machine works on a principle of two metal objects hitting each other at a speed of 50 miles per hour. This is the inner workings of the machine. It works on an air gun principle making one piece of metal hitting into another at the speed of fifty miles per hour. This creates a shock wave that is transferred to the tissue. AS I have previously mentioned there are also other types of machines generate shock waves in different fashion. But the machine I just mentioned is the type I am most familiar with and the one I use.
What the shock wave actually does is create a bit of trauma to the area. This trauma also releases growth factors. In some respects, this is similar to those physicians that are proponents of Prolotherapy or for that matter PRP therapy. In Prolotherapy, some type of irritant such as high concentrations of dextrose (essentially sugar water) is injected into a tendon area or a joint. The idea is that the irritating solution will cause an inflammation. The inflammation will elicit certain cells in our immune system to secrete certain growth factors which attract stem cells. We now have the cascade of healing.
These growth factors are what seems to begin the cascade of healing. When ESWT is performed it releases among other factors Vascular Endothelial Growth Factor (VEGF). VEGF is responsible for creating a vascular supply where there typically the supply is deficient. The lack of a vascular supply is what helps to cause many problems such as tendinosis. Tendinosis is a chronic problem that the body has given up on healing. Tendinitis is more of an acute problem. It is also thought that the ESWT releases certain growth factors that enable stem cell homing to a certain area. Homing is the principle where stem cells have a beacon to injured areas. This has been demonstrated by some fairly nifty experiments. In these experiments, stem cells were tagged with a tracer and were then injected into the body via an intravenous route. It was found that the cells seemed to congregate to the areas where the shock wave therapy was performed. Another growth factor produced is (PCNA) Proliferating Cell Nuclear Antigen. PCNA can help the cell repair its DNA etc.
Another important aspect of shock wave therapy is the formation of Nitric Oxide. Actually, shock wave therapy produces an enzyme which is responsible for the formation of Nitric Oxide. This enzyme is called eNOS or endothelial Nitric Oxide synthase. Among other things eNOS is the mechanism by which hyperbaric oxygen has its success. The eNOS stimulates the formation of Nitric Oxide in the bone marrow. This Nitric Oxide than stimulates the bone marrow to release large numbers of stem cells into the circulation. The eNOS will also stimulate the formation of blood vessels in tissues where there seems to be a lack of blood flow. This is very typical of an area of injury such as a chronic tendinosis. We are now starting to realize that Nitric Oxide (NO) is one of the holy grails of stem cell therapy. NO has many different tasks in the body. It depends somewhat on what “neighborhood” in the body we find the Nitric Oxide in. The neighborhood effects its actions. We now know that NO is an extremely important signaling molecule in the body. It is known to be a growth, immune, and neuromodulator as well as a stimulator of stem cell proliferation. It has critical roles in analgesia, vasodilation and ATP production. NO release in the body is caused by many different factors. When we start combining shock wave therapy with laser therapy than we may stimulate significant amounts of NO. Laser therapy is similar to shock wave therapy in that it seems to have profound effects on the cell environment. Laser therapy will be the subject of another article.
By utilizing shock wave therapy with the some the regimens that we already have hopefully many good things will happen. Using shock wave therapy with Platelet Rich Plasma (PRP) and or Stem cells will dramatically improve results.
I do not know if shock wave therapy itself will be total game changer but I do know it will be an increasingly important part of our ever-expanding armamentarium of treatments. I am sure there will be more to come concerning this modality. I believe this will become an increasingly important aspect in the utilization of PRP and Stem cell therapy in the treatment of hip, knee, spine and other musculoskeletal problems. Thanks, Dr. P.