Electrical Muscle Stimulation (EMS or E-Stim) has most commonly been used for the modulation of pain through stimulation of cutaneous sensory nerves and following analgesic mechanisms:
- Activation of large diameter nerve fibers inhibits the pain transmissions carried from the spinal cord to the brain - also known as the gate control theory of pain.
- Stimulation of specific nerve fibers causes the release of endogenous opioids (endorphin and enkephalin) resulting in prolonged activation of descending analgesic pathways.
Ultrasound utilizes sound energy, pressure waves created by the mechanical vibration of particles through a medium. The flow of ultrasound may be delivered as an uninterrupted stream (continuous mode) or delivered with periodic interruptions (pulsed mode). Ultrasound is classified as a deep heating modality capable of producing a temperature increase in tissues of considerable depth because it travels very well through homogenous tissue (e.g. fat tissue). Traditionally it has been used for its thermal effects but it is capable of enhancing healing at the cellular level. Continuous ultrasound is most commonly used when thermal effects are desired but non-thermal effects will also occur. It has been shown to alter all phases of tissue repair:
- Stimulates phagocytic activity of inflammatory cells such as macrophages
- Promotes release of chemical mediators from inflammatory cells which attract and activate fibroblasts to the site of injury
- Stimulates and optimizes collagen production
- organization and ultimately functional strength of scar tissue
Ultrasound also aids in pain relief through reduced conduction of pain transmission as a possible mechanism for the analgesic effects. More recently, low-intensity pulsed ultrasound has been shown to accelerate the rate of healing of fresh fractures due to the enhancement of angiogenic, chondrogenic, and osteogenic activity.