Extracorporeal shock wave (ESW) therapy is the use of highly energetic sound waves to "hit" diseased tissues. Originally it was developed to treat kidney stones, lithotripsy, by breaking them up. ESW has been used to treat some orthopedic conditions in people for a few years and recently has been used in horses. Conditions treated in the horse include: proximal suspensory desmitis including avulsion fractures of its insertion, bucked-shins, tibial stress fractures, proximal sesamoid bone fractures, incomplete proximal phalangeal fractures, subchondral bone pain, suspensory branch insertions, impinging dorsal spinous processes, osteoarthritis of the distal hock joints, navicular disease, and more recently digital flexor tendonitis. While originally the use was reserved for conditions involving bone or the insertion of soft tissue on bone more recently some work with purely soft tissues has begun. This article describes the process of ESW, some of the variables in treatment and describes what is known about the efficacy of the procedure.

ESW are powerful sound waves generated by a machine that uses a probe to transmit the shock wave into the tissues. The sound waves would look like ocean waves with peaks and troughs of pressure flowing through the tissues.

More Information on What is a joule? A unit of energy; the heat generated, or energy expended, by an ampere flowing through an ohm for 1 sec; equal to 107 ergs and to a newton-meter. It is an approved multiple of the SI fundamental unit of energy, the erg, and is intended to replace the calorie (4.184 J)

The amount of energy generated over an area is an important when judging treatment and can be varied. It is usually expressed in milliJoules per square millimeter (mJ/mm squared). Also important are the duration and frequency of the pulses. Still other important factors are whether the shock waves can either be focused or radial. Focused waves converge on a single point, concentrating the energy on the desired target. Focused machines also have variable energy settings. Radial waves weaken as they leave the machine, exposing more peripheral tissue and delivering less energy less deeply to the diseased tissues. Focused shock wave machines are considerably more expensive but are smaller so more mobile.

Though there are theories about how ESW might work the mechanism of action remains unknown. All of these theories revolve around the idea of producing a controlled trauma that induces a inflammatory reaction followed by a boosted healing response. Parts of the this response may include increased blood flow, unknown cellular effects, and activated bone growth factors. It should be noted that shock waves cause a well established temporary nerve block and so may provide pain relief to tissues that may not be strong enough to be exercised.