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Physiotherapy: therapeutic ultrasound
Introduction
- Therapeutic ultrasound is a physiotherapy treatment that uses high-frequency sound waves to produce both thermal and non-thermal effects in mainly soft tissue structures to improve healing and remodeling of injuries.
- It is particularly useful in improving wound healing, remodeling scar tissue, reducing edema and soft tissue filling in limbs, improving flexibility of movement after injury and fibrosis, and treating muscle injuries.
Uses
- As part of a physiotherapy regimen Physiotherapy - can shorten rehabilitation time, decrease swelling/edema and pain, and facilitate increase in motion:
- Remodeling of scar tissue and facial planes Wound: secondary intention healing.
- Promotion of wound healing Wound: healing - stages by increasing protein synthesis in fibroblasts (use at least two weeks post-injury) Wound: healing - factors.
- Osteoarthritis Arthritis: osteoarthritis - promotes healing and flexibility of the joint capsule. There may also be some affect on the synovial membrane.
- Tendon injuries. Studies have shown improved histological appearances of damaged tendons and less peritendinous adhesions.
- Muscle damage and spasm/pain.
- Resolution of tissue edema and hematomas once hemorrhage has stopped.
- Nerve injuries by encouraging remyelination and regeneration of damaged axons.
- Phonophoresis: to facilitate dispersal of topical or injected medications throughout soft tissues:
- Anti-inflammatory agents Therapeutics: musculoskeletal, eg following intra-articular injection Anesthesia: intra-articular → aids in distributing agent evenly throughout joint capsule.
Advantages
- Non-invasive technique.
- Wide range of applications.
- Easy to apply once instructed by trained person such as physiotherapist. Owners may be able to treat the animal under instruction saving costs and increasing frequency of treatment.
Disadvantages
- Tissues can be damaged if ultrasound is used inappropriately - it should only be used in those cases where there has been a full veterinary evaluation.
- Tissue damage can be done before there is a pain response in the patient.
- Should not be used in proximity to open wounds or metal implants, or in cases of cellulitis Skin: cellulitis, infection, unstable fractures or surgical incisions.
Alternative techniques
- See specific clinical problems for alternative treatments.
- See also physiotherapy techniques Physiotherapy.
Contraindications
- Should not be applied to the eye - poor vascularization → overheating.
- Over uterus during pregnancy - may be mutagenic.
- Over reproductive organs.
- Over the brain.
- Growth plates should be avoided until they have closed.
- Over the heart can alter action potentials and contractile properties in cardiac tissue.
- Use near tumors may promote metastasis.
- In areas where there is vascular insufficiency or substantial vascular abnormalities.
- In tissues with decreased sensation/anesthetized.
- In proximity to open wounds, tissues that are bleeding, surgical incisions or metal implants; or in cases of cellulitis, infection, or fractures (may delay healing).
- Application immediately after exercise as tissues already at elevated temperature.
Mechanism of action
- There are basically two effects of ultrasound when it is passed through tissues: thermal and non-thermal.
- Thermal effects on tissues are more likely where the sound waves are continuous. Pulsed emission may reduce the possibility of thermal changes while maintaining the beneficial non-thermal effects. Typical pulse ratios are 1:1 (output of US occurs for 2 min followed by 2 min of rest) and 1:4 (output for 2 min followed by an 8 min rest).
- Sound energy is impeded by passage through tissues and this varies with the density and elasticity of the tissue, therefore tissue type will effect impedence, eg there will be a difference between muscle compared with fat. Some of the sound energy is converted to thermal energy within tissues, this heat has the effects of increased metabolic rate, increased membrane permeability, vasodilation, decreased muscle spasms, increased pain threshold, increased collagen extensibility and hindering of neural transmission of pain impulses.
- Ultrasound energy is particularly absorbed by collagenous structures such as periosteum, ligaments, fascia, scar tissue; less so by synovial tissue, menisci and joint capsules, and even less by nervous tissue and muscle. The skin absorbs relatively little, and cartilage and bone reflect a large proportion of US energy. Therefore, the thermal related therapeutic effects are more common in the periosteum, collagenous tissue (ligaments, tendon, fascia), and fibrotic muscle. If the temperature of the damaged tissue is raised to 40-45°C/104-113°F there is hyperemia, which can be therapeutic and help resolve chronic inflammation and fibrosis.
- Excessive exposure to ultrasound may cause thermal injury.
- High frequency vibrational energy creates non-thermal effects which are caviation (the formation of gas filled voids or bubbles in tissue and body fluids) and acoustic streaming (affects cell diffusion rates and membrane permeability). The result of both of these effects is that the cell membranes of cells within treated tissues become up-regulated and more active thereby causing a therapeutic effect. It is now thought this may be of greater benefit than the thermal effects and is the preferred method of application.
- Output power, frequency, ultrasound beam profile, and temporal aspects of the sound emission influence the therapeutic effect, and all of these need to be considered before establishing a protocol for US treatment.
- Penetration is inversely proportional to the ultrasound wave frequency and as ultrasound wave frequency increases so depth of penetration decreases.
- Measurement of the depth of tissue at which half the surface energy is available and is different for each tissue type and US frequency. Tissues with high protein content are the greatest absorbers whilst those with high water content absorb very little. Therefore, the depth from the skin and the type of tissue to be treated will affect the individual settings of the machine. The average half value depths for the main frequencies that are used are 3 MHz = 2 cm; 1 MHz = 4 cm.
- The half value depth represents a measurement of the depth of tissue at which half the surface energy is available An air gap severely decreases any penetration of the beam into the underlying tissue. Coupling media such as water, oils, creams and gels are used to help bridge this air gap. Specifically made coupling gels or water are recommended.
- Ultrasound treatment should be avoided during the acute phase of inflammation.
- Periosteal overheating can occur when bone is exposed to ultrasound, from direct exposure and internally reflected energy.
- Therapeutic ultrasound is known to have a number of effects on soft tissue injuries and their repair, and an understanding of these effects should help determine when this technique may be of use:
- During the proliferative or scarring phase of inflammation, US promotes proliferation by upregulating fibroblasts, endothelial cells and myofibroblasts. This leads to increased protein and collagen synthesis, which enhances fibroplasia. This may help to produce the required scar in the most efficient manner.
- In the remodeling phase of repair, therapeutic US increases the tensile strength, mobility and function of scar tissue by improving collagen fiber orientation and changing type III collagen to type I.
- Therapeutic US also has an analgesic effect probably via decreased local nerve conduction and the release of endorphins and serotonin.
Time required
Preparation
- 5-10 min to clip and clean the area for treatment.
Procedure
- Usually 5-10 min sessions.
- Usually daily sessions for 10-14 days, depending on rate of response followed by 2-4 sessions per week until resolution.
Requirements
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Preparation
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Technique
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Aftercare
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Outcomes
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Further Reading
Publications
Refereed Papers
- Recent references from PubMed and VetMedResource.
- Saini N S et al (2002) A preliminary study on the effect of ultrasound therapy on the healing of surgically severed achilles tendons in five dogs. J Vet Med Physiol Pathol Clin Med 49 (6), 321-328 PubMed.
- Lang D C (1980) Ultrasonic treatment of musculoskeletal conditions in horse, dog and cat. Vet Rec 106 (21), 427-431 PubMed.
Other sources of information
- Ball M A (2003) Therapeutic use of Ultrasound, Lasers and Electromagnetics. In: Diagnosis and Management of Lameness in the Horse. Eds: Ross R W & Dyson S J. Saunders, Missouri. pp 811-812.
- Porter M (1999) Therapeutic Ultrasound. In: Equine Medicine and Surgery. Eds: Colahan P T, Mayhew I G, Merritt A M & Moore J N. Mosby, Missouri. pp 1444-1446.