Horses should be rested for at least two days after (focused) shock wave therapy to prevent further injury, warn vets at Iowa State University. Their studies have shown that horses with chronic forelimb lameness improve after treatment with focused extracorporeal shockwave therapy.
Extracorporeal shock wave therapy (ESWT) is a popular treatment for some musculoskeletal disorders in the horse. It seems to be particularly useful for injuries involving the junction of ligaments or tendons to bone.
Two types of shock wave therapy are used. In focused extracorporeal shock wave therapy (ESWT) the pressure waves are focused at a point within the tissues. Shock waves are of very short duration (1 microsecond) and can reach pressures of up to 100MPa.
In the second type, known as radial pressure wave therapy (RPWT) the shock waves are not focused. They are at their most powerful where the head of the therapy unit contacts the body. From there, the waves spread out into the tissues. The characteristics of the pressure waves generated by this type of unit are completely different to those of ESWT. The maximum peak pressure is much lower (about 7MPa) and the duration of the pressure pulse is greater (more than about 4 microseconds)
The force of the shock waves on the target tissues varies significantly depending on whether focused or non-focused waves are used. This is likely to account for some of the conflicting reports about the effects of shock wave therapy.
Some evidence suggests that shock wave therapy has an analgesic effect. This may result in overuse of the damaged limb, leading to further injury. Because of this concern, some racing authorities have banned shock wave therapy in horses within 7 days of racing.
Jessica Dahlberg, with Dr Scott McClure and others at the College of Veterinary Medicine at Iowa State University, have been assessing the effect of a single treatment of ESWT on forelimb lameness. They used force plate measurements to give an objective assessment of the degree of lameness.
They looked at nine horses in the study. All had a long-term lameness of one forelimb. Six had been diagnosed with navicular syndrome. Three had osteoarthritis. None had received any anti-inflammatory or pain-relieving medication for 14 days before the start of the study.
Horses were trotted in hand down a track with a force plate embedded in it. The researchers recorded the peak vertical force, and the vertical impulse. These are measures of how heavily the horse lands on the leg. An increase in their value indicates an improvement in the lameness.
Force plate recordings were made before and after ESWT and after local anaesthesia to eliminate the lameness.
The horses showed a gradual improvement in lameness, which peaked two days after treatment. In fact, after shock wave therapy, the peak vertical force was similar to when the lameness was abolished with local anaesthetics.
The pain -reliving effect of the single shock wave treatment was short -lived. All horses were as lame at the end of the seven-day study as they were at the beginning.
As only horses with long-term lameness had been used in the study, the researchers could not tell whether a similar analgesic effect would be seen in horses with lameness of lesser duration. Neither did they assess the effect of more than one treatment.
However, they did find that horses with naturally occurring forelimb lameness show an improvement in lameness for at least two days after ESWT. So Dr McClure recommends that horses undergoing ESWT should be restricted to controlled exercise for at least 2 days after treatment.
For more details see:
Force platform evaluation of lameness severity following extracorporeal shock wave therapy in horses with unilateral forelimb lameness.
Jessica A Dahlberg, Scott R McClure, Richard B Evans, Eric L Reinertson.
JAVMA (2006) 229, 100 - 103