Shockwave Therapies in Soft Tissue Conditions
Shockwave Therapies in Soft Tissue Conditions
Extracorporeal shockwave therapy (ESWT) has been used in the treatment of soft tissue and bone-related musculoskeletal disorders for over 20 years. In an overview of this treatment modality by this author in 2004, the heterogeneous evidence base and the diversity of treatment types and protocols that were in use were discussed. At that time, there was evidence of benefit of focused ESWT (F-ESWT) in the treatment of calcific rotator cuff tendinopathy and in plantar fasciitis. In the time ensuing, although there has been much research activity and an expansion in publications, interpreting the current literature has become even more challenging. This in part relates not only to the study design and study populations but also to the increasing array of shockwave (SW) systems, treatment protocols and, importantly, basic differences in forms of 'shock waves' used. The aims of this update were to summarise and clarify the current evidence base relating to ESWT, current treatment systems and the differences between different forms of therapy.
SWs are three-dimensional pressure pulses of microsecond duration with peak pressures of 35–120 MPa. The more established form of medical ESWT involves focused SWs. These are concentrated into small focal areas of 2–8 mm diameter in order to optimise therapeutic effects and minimise effects on other tissues. Many of the physical effects are considered to be dependent on the energy delivered to a focal area. The concentrated SW energy per unit area, the energy flux density, (EFD, in mJ/mm), is a term used to reflect the flow of SW energy in a perpendicular direction to the direction of propagation and is taken as one of the most important descriptive parameters of SW 'dosage'. There remains no consensus as to the definition of 'high and 'low' energy ESWT, but as a guideline, low-energy ESWT is EFD≤0.12 mJ/mm, and high energy is >0.12 mJ/mm.
Focused SW systems differ in their design and in particular whether the SWs are generated by electrohydraulic, electromagnetic or piezoelectric mechanisms (Table 1). The waveform characteristics, focal area and tissue penetration of SWs—and hence their effects on tissue—are influenced by this. Regardless of the method of SW generation, SWs are concentrated by means of focusing reflectors to the target site. The proposed mechanisms for the benefit of F-ESWT on musculoskeletal tissue include direct effects on tissue calcification, alteration of cell activity through cavitation, acoustic microstreaming, alteration of cell membrane permeability and effects on nociceptors through hyperstimulation, blocking the gate control mechanism.
Another form of treatment, often described as 'radial shock wave therapy', is better termed 'radial pulse therapy' (RPT). Some studies of 'low energy ESWT' are in fact referring to the use of RPT. Their description as SWs is inappropriate and has caused much confusion in interpreting the literature. Radial 'shock' waves are generated by a ballistic source and do not have the characteristics of real medical SWs. They are not focused and it has been demonstrated that they do not have a penetrating effect on tissue, but rather act superficially. The mechanisms of action of RPT on musculoskeletal tissues are as yet unclear. The increasing popularity of radial 'shock' wave systems is predominantly related to their lower cost.
No direct comparison of F-ESWT with RPT has been performed, although a study design for such a trial in patella tendinopathy has been published.
Background
Extracorporeal shockwave therapy (ESWT) has been used in the treatment of soft tissue and bone-related musculoskeletal disorders for over 20 years. In an overview of this treatment modality by this author in 2004, the heterogeneous evidence base and the diversity of treatment types and protocols that were in use were discussed. At that time, there was evidence of benefit of focused ESWT (F-ESWT) in the treatment of calcific rotator cuff tendinopathy and in plantar fasciitis. In the time ensuing, although there has been much research activity and an expansion in publications, interpreting the current literature has become even more challenging. This in part relates not only to the study design and study populations but also to the increasing array of shockwave (SW) systems, treatment protocols and, importantly, basic differences in forms of 'shock waves' used. The aims of this update were to summarise and clarify the current evidence base relating to ESWT, current treatment systems and the differences between different forms of therapy.
ESWT: Definitions
SWs are three-dimensional pressure pulses of microsecond duration with peak pressures of 35–120 MPa. The more established form of medical ESWT involves focused SWs. These are concentrated into small focal areas of 2–8 mm diameter in order to optimise therapeutic effects and minimise effects on other tissues. Many of the physical effects are considered to be dependent on the energy delivered to a focal area. The concentrated SW energy per unit area, the energy flux density, (EFD, in mJ/mm), is a term used to reflect the flow of SW energy in a perpendicular direction to the direction of propagation and is taken as one of the most important descriptive parameters of SW 'dosage'. There remains no consensus as to the definition of 'high and 'low' energy ESWT, but as a guideline, low-energy ESWT is EFD≤0.12 mJ/mm, and high energy is >0.12 mJ/mm.
Focused SW systems differ in their design and in particular whether the SWs are generated by electrohydraulic, electromagnetic or piezoelectric mechanisms (Table 1). The waveform characteristics, focal area and tissue penetration of SWs—and hence their effects on tissue—are influenced by this. Regardless of the method of SW generation, SWs are concentrated by means of focusing reflectors to the target site. The proposed mechanisms for the benefit of F-ESWT on musculoskeletal tissue include direct effects on tissue calcification, alteration of cell activity through cavitation, acoustic microstreaming, alteration of cell membrane permeability and effects on nociceptors through hyperstimulation, blocking the gate control mechanism.
Another form of treatment, often described as 'radial shock wave therapy', is better termed 'radial pulse therapy' (RPT). Some studies of 'low energy ESWT' are in fact referring to the use of RPT. Their description as SWs is inappropriate and has caused much confusion in interpreting the literature. Radial 'shock' waves are generated by a ballistic source and do not have the characteristics of real medical SWs. They are not focused and it has been demonstrated that they do not have a penetrating effect on tissue, but rather act superficially. The mechanisms of action of RPT on musculoskeletal tissues are as yet unclear. The increasing popularity of radial 'shock' wave systems is predominantly related to their lower cost.
No direct comparison of F-ESWT with RPT has been performed, although a study design for such a trial in patella tendinopathy has been published.
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