- Therapeutic ultrasounds use sound waves to reduce pain, decrease inflammation, and promote healing in injured tissues.
- Ultrasound therapy can warm deep tissues to relax muscles and increase flexibility, or stimulate cell repair.
- Your physical therapist carefully selects ultrasound settings like frequency and mode to best suit your specific condition.
- During treatment, a moving probe with gel is applied to your skin, sometimes feeling gentle warmth.
Table of Contents
Ultrasounds in physiotherapy
Therapeutic ultrasounds are one of the most widely used instrumental physical therapies in physiotherapy and rehabilitation. They utilize high-frequency sound waves (from 1 to 3 MHz), inaudible to the human ear, which penetrate tissues producing thermal and non-thermal effects with analgesic, anti-inflammatory, and biostimulating purposes. This is an established technology, used for over 60 years, economical, and widely available in physiotherapy clinics. Their effectiveness, however, depends on the correct choice of parameters and appropriate clinical indication.
How They Work
Physical principle
The ultrasound probe (transducer) contains a piezoelectric crystal which, when traversed by alternating electric current, vibrates, producing high-frequency sound waves. These waves penetrate tissues and are absorbed differently by various tissue types.
Therapeutic effects
Thermal effects (continuous mode):
- Increase in local tissue temperature (up to +4°C in depth)
- Increase in local blood flow and metabolism
- Increase in the extensibility of collagen tissue (tendons, capsules, scars)
- Muscle relaxant effect
- Pain reduction by stimulating thermoreceptors
Non-thermal/mechanical effects (pulsed mode):
- Stable cavitation: formation and oscillation of gas microbubbles in tissues, stimulating cell membranes
- Acoustic streaming: unidirectional flow generated by sound waves, which modifies cell membrane permeability
- Stimulation of cell proliferation and protein synthesis
- Increase in cell membrane permeability (promotes the passage of nutrients and drugs)
- Anti-inflammatory effect and stimulation of healing
Treatment Parameters
| Parameter | Options | Indication |
|---|---|---|
| Frequency | 1 MHz | Deep tissues (3-5 cm): muscles, joints |
| 3 MHz | Superficial tissues (1-2 cm): tendons, superficial ligaments | |
| Mode | Continuous | Predominant thermal effect — stiffness, contractures, scars |
| Pulsed | Non-thermal effect — acute phase, inflammation, edema | |
| Intensity | 0.5-1 W/cm² | Superficial structures, subacute phase |
| 1-2 W/cm² | Deep structures, chronic phase | |
| Duration | 5-10 minutes | Per treated area |
| Session frequency | 3-5 times/week | Cycle of 8-12 sessions |
Application Techniques
Direct contact technique
The most common technique:
- Application of coupling gel on the area to be treated
- The probe is moved over the skin with slow, overlapping circular movements
- The probe must always be in motion to avoid energy concentrations (hot spots) that could cause pain or tissue damage
- Speed: approximately 4 cm/second
Underwater technique
Used to treat irregular surfaces and small joints (hand, foot, ankle):
- The area to be treated is immersed in lukewarm water (basin)
- The probe is held 1-2 cm away from the skin
- Water acts as a conduction medium
- Useful for treating the hand, wrist, foot, and ankle
Phonophoresis
Use of ultrasounds to promote the penetration of drugs through the skin:
- A gel containing the drug (anti-inflammatory, corticosteroid) is applied instead of the standard coupling gel
- Ultrasounds increase skin permeability, promoting transcutaneous absorption
- Evidence on the additional efficacy of phonophoresis compared to ultrasounds alone: moderate
Indications
Tendon pathologies
- Chronic tendinopathies: Achilles, patellar, rotator cuff
- Epicondylitis and epitrochleitis
- Calcific tendinitis: ultrasounds can contribute to the reabsorption of calcifications
- Mode: pulsed in the acute-subacute phase, continuous in the chronic phase
Joint pathologies
- Osteoarthritis: knee, hip, hand, spine
- Adhesive capsulitis of the shoulder: before mobilization to increase capsular extensibility
- Post-immobilization joint stiffness: in combination with manual therapy
- Arthritis (in non-acute phases)
Soft tissue pathologies
- Muscle contractures: thermal effect for muscle relaxation
- Scars and adhesions: thermal and mechanical effect to improve extensibility
- Organized hematomas (late phase)
- Subacute and chronic bursitis
- Carpal tunnel syndrome
Tissue healing
- Fractures: acceleration of consolidation (low-intensity pulsed ultrasound, LIPUS)
- Ulcers and wounds: stimulation of healing (proliferative phase)
- Ligamentous injuries: in the subacute-chronic phase
Contraindications
Absolute
- Neoplasms in the area to be treated
- Deep vein thrombosis or phlebitis in the area
- Pregnancy over the abdominal and lumbar region
- Metallic implants in the area (risk of overheating — controversial with modern materials)
- Tissues with poor vascularization or ischemic tissues
- Bone growth plates in children
- Eyes, testicles, gravid uterus
Relative
- Pacemaker: do not irradiate the thoracic region
- Active infections: risk of spread
- Areas with reduced sensitivity: risk of unperceived burn
- Joint prostheses: caution, use pulsed mode at low intensity
Scientific Evidence
Therapeutic ultrasound uses high-frequency sound waves (1-3 MHz) to generate thermal and mechanical effects in tissues, promoting healing, reducing inflammation, and improving mobility in musculoskeletal conditions. The evidence on therapeutic ultrasounds is variable and subject to debate in the scientific community.
Positive evidence:
- LIPUS (low-intensity pulsed ultrasound) for fracture consolidation: solid evidence for accelerating healing, especially in fractures at risk of delayed consolidation
- Adhesive capsulitis: in combination with exercises, improves ROM
- Epicondylitis: short-term analgesic effect
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Moderate evidence:
- Chronic tendinopathies: efficacy as a complement to exercise
- Knee osteoarthritis: modest pain reduction
- Carpal tunnel: symptomatic improvement in combination with a brace
Limited evidence:
- Chronic low back pain: uncertain benefit
- Acute muscle injuries: not sufficient as an isolated treatment
Note: As with most instrumental therapies, ultrasounds are more effective in combination with therapeutic exercise and manual therapy, not as an isolated treatment.
Advantages and Limitations
Advantages
- Non-invasive and generally painless
- Established technology and widely available
- Versatile: applicable to numerous pathologies
- Low cost per session
- Combinable with other therapies (e.g., before manual therapy to prepare tissues)
Limitations
- Modest efficacy as an isolated treatment
- Operator technique dependence: the probe must always be in motion, parameters must be correct
- Limited penetration: very deep structures are difficult to reach
- Scientific evidence not always solid: for some indications, efficacy is uncertain
Frequently Asked Questions (FAQ)
No, ultrasound therapy is generally painless. In continuous mode, a slight pleasant warmth may be felt. If pain is felt, the intensity should be reduced or switched to pulsed mode. Pain during treatment may indicate incorrect application.
A standard cycle includes 8-12 sessions, with a frequency of 3-5 times a week. The exact number depends on the pathology and the patient’s response. The first benefits are generally felt after 4-5 sessions.
No, even though they use the same physical principle (sound waves). An ultrasound scan is a diagnostic examination that uses very low-power ultrasounds to produce images of tissues. Therapeutic ultrasounds use higher powers to produce biological effects (thermal and mechanical) in tissues.
The issue is debated. With modern metallic prostheses (titanium, surgical steel), ultrasound therapy in pulsed mode at low intensity is generally considered safe. Continuous mode at high intensity should be avoided due to the risk of overheating at the bone-metal interface. The decision is made by the physical therapist based on the specific case.
Yes, low-intensity pulsed ultrasounds (LIPUS) have been shown to accelerate fracture consolidation, especially in cases of delayed consolidation. They are applied with a specific protocol (20 minutes/day) and with dedicated devices. The efficacy is supported by solid scientific evidence.
Frequently Asked Questions
What are the primary therapeutic effects of ultrasound therapy?
Therapeutic ultrasounds utilize sound waves to produce both thermal and non-thermal effects within tissues. These effects contribute to reducing pain, decreasing inflammation, and promoting the healing of injured tissues. Additionally, ultrasound therapy can warm deep tissues to relax muscles, increase flexibility, and stimulate cellular repair processes.
For which conditions are therapeutic ultrasounds typically indicated?
Therapeutic ultrasounds are commonly indicated for a range of musculoskeletal conditions affecting tendons, joints, and soft tissues. They are also utilized to support tissue healing processes following injury. A physical therapist assesses each individual case to determine the most appropriate application.
How does a physical therapist select the correct parameters for ultrasound treatment?
A physical therapist carefully selects ultrasound parameters, such as frequency and mode, based on the specific condition being treated and the desired therapeutic outcome. Factors like the depth of the target tissue, the stage of injury, and the presence of inflammation guide these choices. This individualized approach ensures the most effective and safe application of the therapy.
Are there any contraindications for receiving therapeutic ultrasound treatment?
Yes, there are specific situations, categorized as absolute or relative contraindications, where therapeutic ultrasounds should not be applied. These may include certain medical conditions or areas of the body. A thorough assessment by a physical therapist is essential to identify any contraindications and ensure the safety of the treatment.
Sources and Scientific References
- As-Sanie S et al. (2025). Endometriosis: A Review. JAMA. 334:64-78. DOI | PubMed
- Wipperman J et al. (2016). Carpal Tunnel Syndrome: Diagnosis and Management. Am Fam Physician. 94:993-999. PubMed
- Del Forno S et al. (2021). Assessment of levator hiatal area using 3D/4D transperineal ultrasound in women with deep infiltrating endometriosis and superficial dyspareunia treated with pelvic floor muscle physiotherapy: randomized controlled trial. Ultrasound Obstet Gynecol. 57:726-732. DOI | PubMed
- Bachu VS et al. (2021). High-Intensity Focused Ultrasound: A Review of Mechanisms and Clinical Applications. Ann Biomed Eng. 49:1975-1991. DOI | PubMed
- Kauwe M (2017). Acute Achilles Tendon Rupture: Clinical Evaluation, Conservative Management, and Early Active Rehabilitation. Clin Podiatr Med Surg. 34:229-243. DOI | PubMed