Shockwave therapy physiological effects

The therapeutic Extracorporeal Shockwave therapy physiological effects have been vindicated by several studies in the recent literature. The physical shockwave impulses delivered by Extracorporeal Shockwave therapy (ESWT) raise the mechanotransduction in the respective musculoskeletal tissues, and convert the acoustic waves into biological signals which lead to a cascade of biological responses in the tendon, bone, and tendon-bone interface tissue. In contrast to lithotripsy, where shockwaves are used to disintegrate urolithiasis (“kidney stones”); and orthotripsy, where shockwaves are used in orthopedics to disintegrate tissues such as osteophytes (“bony outgrowths”); the function of ESWT resides in tissue regeneration at a cellular level, although ESWT have been shown to also serve as orthotripsy. Several studies have been conducted to investigate the biological mechanism of musculoskeletal shockwaves via the ESWT. These studies entailed clinical experiments in comparison to controls/ placebos; histomorphological examinations; immunohistochemistry analysis; and the biological responses to the shock wave intervention; independently in tendon, bone and the bone-tendon interface:

Effect on tendon tissue: A single application of ESWT with 500 impulses at 14 KV was applied to the Achilles tendon near its insertion at the calcaneus in rabbits compared to a control group. Biopsies with the respective histomorphological examination were applied thereafter immediately at 24 hours, week 1, 4, 8 and 12. The respective immunohistochemistry analysis was applied to all specimens; angiogenic growth markers were examined to confirm neovascularization in the tendon tissue, including vessel endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS); as well as proliferating cell nuclear antigen (PCNA) to reflect endothelial cell proliferation. The results demonstrated post-ESWT compared to the control group; a significant increase in the number of gross neo-vessels at 4 to 12 weeks (p<0.05); a significant increase in the number of VEGF and eNOS expressions at week 4 to 8 (p<0.05); and the expression of PCNS showed a significant increase at week 1 to12 weeks (p<0.05). The control showed no significant change in all variables (p>0.05). This study may provide the scientific evidence that ESWT stimulates the early release of VEGF, eNOS and PCNA expressions with subsequently ingrowth of neo-vessels (angiogenesis) in tendon tissue, stimulates tendon repair and growth, and significantly reduces tendon healing time. Shock wave therapy cause new small blood vessels to form in the injured tissue to improve blood supply and thereby significantly promote healing of the tendon (and bone).

In addition, ESWT has been found to cause the dissolution of calcified fibroblasts in tendon tissue. Shock wave therapy breaks up calcium build-up in injured tendons which is often the result of micro-tears or other trauma, and thereby significantly reduces joint and muscle pain particularly in the chronic setting.

Effect on bone tissue: A single application of ESWT was applied to an induced closed fracture of the femur one week after the surgical wounds have healed in rabbits. The sample consisted of a control group, a group which received low-energy shock wave with 4000 impulses at 14 KV, and a group which received high-energy shock waves with 4000 impulses at 14 KV. Biomechanical examination with the respective application of histomorphological examination commenced at 12 weeks and entailed the harvesting of a 5-cm long femur bone including the callus. The specimens in all groups were subjected to biomechanical testing on Material Testing System including peak load, peak stress, and modulus of elasticity. The respective immunohistochemistry analysis was applied; angiogenic growth markers were examined to confirm neovascularization in the bone tissue, including VEGF, eBOS, PCNA, and bone morphological protein (BMP-2); as well as an antibody against von Willebrand factor (vWF) to identify the immunolocalization of neo-vessels in the fracture site. The results demonstrated post-ESWT with the high-energy shock waves compared to the low-energy shock waves and control group; a significant increase in the number of gross neo-vessels in the fracture site (p<0.05), with a significant increase in the number of VEGF, eNOS, PCNA, BMP-2 and vWF expressions (p<0.05); the morphological increase in cortical bone at the fracture site and less fibrous tissue and comparable woven bone; and the biomechanical increase in bone strength, including peak load, peak stress and modules of elasticity. The control and low-energy shock wave groups showed no significant change in all variables (p>0.05). This study may provide the scientific evidence that ESWT stimulates the early release of VEGF, eNOS, PCNA, BMP-2 and antibody against vWF expressions with subsequently ingrowth of neo-vessels in bone tissue, stimulates cortical bone repair and growth, and significantly reduces fracture healing time. Shock wave therapy significantly promotes healing of a broken bone, decrease the formation of scar tissue, and increase bone strength.

Effect on tendon-bone interface tissue: A single application of ESWT with 500 impulses at 14 kV was applied to a knee with induced anterior cruciate ligament reconstruction immediately after the operation in rabbits compared to a control group; the shockwave impulses were directed to the tendon graft proximal to the tibia. Biomechanical examination with the respective application of histomorphological examination commenced at week 1, 2, 4, 8, 12 and 24; and entailed the harvesting of the tendon graft and portion of the surrounding bone. All specimens were subjected to slow load distraction curve on Material Testing Machine to measure the tensile strength of the graft; as well as the failure load and the modes of failure were analysed to measure the pullout strength of the graft. The respective immunohistochemistry analysis was applied; antigenic growth markers were examined to confirm neovascularization in the graft and surrounding bone tissue, including VEGF, eNOS, PCNA and BMP-2; as well as an antibody against vWF to identify the immunolocalization of neo-vessels in the graft site. The results demonstrated post-ESWT compared to the control group; a significant increase in the number of gross neo-vessels at the tendon-bone interface at week 4 to 24 (p<0.05); a significant increase (p<0.05) in the number of expressions of VEGF at week 4, 8 and 24, BMP-2 at week 4 and 8, eNOS at week 1 and 2, and PCNA at week 12; the amount of trabecular bone around the tendon graft increased significantly after 4 weeks (p<0.05); a morphological increase at the tendon-bone interface after 4 weeks, with a significant increase in the percentage of bonding between the tendon graft and surrounding bone (p<0.05); and the biomechanical increase in tensile strength and superior pullout failure load of the tendon graft. The control showed no significant change in all variables (p>0.05). This study may provide the scientific evidence that ESWT stimulates the early release of VEGF, eNOS, PCNA, BMP-2 and antibody against vWF expressions with subsequently ingrowth of neo-vessels in the tendon-bone interface as well as in a tendon graft, and significantly reduces tendon/ graft repair healing time. Shock wave therapy significantly promotes healing of torn tendons and post-operative tendon repairs.

Effect on pain: ESWT decreases chemokine and cytokine expressions, particularly reduces substance P concentration, as well as increase mast cell activity. In addition, ESWT inhibit nociceptive relay neurons in the dorsal horn by stimulating the Aβ-fiber afferents of mechanoreceptors in the respective tissue. Shock wave therapy significantly reduces pain in the acute and chronic setting, reduces chronic inflammation, and restores the normal healing and regenerative processes.

Effect on tight and sore muscles: Studies have provided the clinical evidence that ESWT have a significant beneficiary effect on myofascial trigger points. The high acoustic energy delivered by the ESWT is postulated to “unblock” the calcium pump and thereby reverse the “metabolic crisis” in the myofilaments and release the trigger points; by promoting angiogenesis, increase perfusion, and altering the pain signalling at the ischemic muscle tissues caused by the possible excessive calcium influx. Trigger points are tight, tender and painful spots in muscles, and are the major cause of muscle pain as well as contribute considerably to joint pain and headaches. Shock wave therapy causes the tight muscle to relax and significantly reduces muscle and joint pain.

 

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