Ultrasound energy is a form of mechanical energy rather than electrical energy. Ultrasound waves induce particles to oscillate around a fixed point as the wave passes through it. As this wave passes through a tissue such as tendon/ligament the wave diminishes as energy is transferred to the tissue. It is this acoustic streaming of the ultrasound beam, in addition to the stable cavitation effects which it induces in tissues, which is beneficial in repairing tissue fibre damage.
This is because the absorption of therapeutic ultrasound achieves maximal effect in dense collagen based tissues such as an injured ligament or tendon, due to the stimulatory effect it has on cellular up-regulation with regards to tissue repair. During the inflammatory stage of repair, ultrasound therapy effectively optimises the inflammatory response, by acting as a pro-inflammatory. Ultrasound doesn’t increase the inflammatory response, but instead, optimises this stage by making the process more efficient, and in doing so enables the tissue to progress onto the next stage of repair (proliferation) sooner.
During the proliferative phase ultrasound energy can stimulate the release of growth factors, up-regulating fibroblastic activity and collagen synthesis. Whilst in the remodelling phase, therapeutic ultrasound promotes realignment of the newly constructed collagen fibres and encourages a change in collagen profile from type 111 to type 1, better representing the 3d construction of un-injured tissue.
Both human and animal literature has supported these claims demonstrating that due to these mechanisms tendon and ligament healing is accelerated, in addition to preventing the formation of adhesions, thus enhancing the tensile stress and functional capacity of the healing tissue.