What causes lowered pain sensation directly after application of shock wave in the treated tissue?

Pathology of pain

• Muscle pain is one of the most common causes of the musculoskeletal disorders requiring treatment.
• Acute pain has also a protective function, meanwhile chronic pain has a significant impact on mentality of the patient.
• Chronic pain is characterised by long lasting (longer than 6 months) and it can become resistant to the treatment.
• Pain occurs with transferred signals from the muscles into the central nervous system with thin and slow nerve fibres.
• The muscles pain be also transferred into the surrounding soft tissues or bones - that is caused by nociceptive signals evoked in a specific segment of the spinal cord, which further increase the irritation of the neurons in the spinal cord.
• In the end it leads to the central increasement of sensitivity.

Focused shock wave

It has an effect on the tissues:

• Increased pressure, tension and specific forces lead to irritation and stimulation of the cells through mechanical deformation of the cytoskeletons. That starts biochemical processes supporting healing.

Radial shock wave

It has an effect on the tissues:

• Radial shock wave (RSW) causes oscillation vibration in the tissues, which leads to improved microcirculation and increasement of metabolic activity.

Application of the shock wave into the muscles

The goal of the shock wave application into the muscle is to lower the pain, lowered muscle tension and stretching the muscles. The effect of the shock wave in the muscles can be simply explained, that a reaction evoked in the tissue can lower the effect of the pathophysiological causes of the local muscle pain.

Exact mechanism of the shock wave effects in muscle treatment is always discussed, several following mechanisms are taken into account:

• Mechanical energy applied in a right angle into the muscle fibres has spatial effect on the sarcomeres and separated fixed actin and myosin fibres (relief of the muscle spasm > better perfusion > lowered pain).
• Evoked neovascularization in connection with bone-tendon connected to relieved factors (synthesis of nitric oxide, vascular endothelial growth factor - present during the healing process, it attracts the endothelial cells into the injured area, and supports their proliferation and angiogenesis), which leads to improved blood supply and tissue regeneration.
• Modulation of the pain thanks to relieved substance P and CGRP (it has effect on the transfer of the pain).
• Selective degeneration of the nerve fibres (which lead informations about the pain).
• Shock wave causes formation of microfractures and microtraumas and eventually it leads to activity of the osteoblasts  and improved healing of the bone.
• Shock wave lowers the pain thanks to the hyper-stimulative analgesics (lowering pain thanks to stimulation of the nerve fibres of bigger diameter with techniques like acupuncture, acupressure, cold compress etc.).
• Mechanism of the shock wave causes cascade of interactions between the physical impulse and tissue, as is depicted in the picture.

The research shows that the focused shock wave - FSW has a therapeutic potential during the treatment of neurological illnesses (e.g. Parkinson’s disease). It affects the increased permeability hematoencephalic barrier, that leads better permeability of the farmaceuticals with bigger molecules (antibiotics, chemotherapeutics etc.). The effect of increased permeability of the hematoencephalic barrier is reversible, we can therefore also lower the risk of possible infections. This potential is needed for inspecting in following studies.

Author: FYZIOklinika physiotherapy Ltd, Prague

Sources: Myofascial Syndromes & Trigger Points, Markus Gleitz, 2011

An Overview of Shock Wave Therapy in Muskuloskeletal Disorders, Ching-Jen Wang, MD, 2003

Fokusovaná rázová vlna způsobuje otevírání hematoencefalické bariéry, Yi Kung et al., 2017