Therapeutic Modalities – Thermal

Overview and Description

Physical Modalities are manually applied agents that yield a specific therapeutic response. This review focuses on both commonly and uncommonly used physical modalities including heat (superficial and deep), cold, sound, electricity, mechanical forces, and light. For other modalities see Therapeutic Modalities – Non-Thermal

Superficial heat

• Superficial heat is the use of a thermogenic agent which induces a temperature increase and subsequent physiologic changes to the superficial layer(s) of the skin, fat, tissues, blood vessels, muscles, nerves, tendons, ligaments, and joints. Superficial heat penetration is usually less than 1 cm.^1,2 In contrast, the use of deep heat penetration is up to about 3-5 cm.²
• Commonly used superficial heat modalities include hot packs, heating pads, paraffin bath, infrared, ultrasound, and fluidotherapy.
• Transfer method: Conduction is transfer of heat between two objects at different temperatures through direct contact (example: hot packs, paraffin bath). Convection is transfer of heat by fluid circulation (liquid or gas) over the surface of a body (example: fluidotherapy). Conversion is the changing of one energy form into another (example: ultrasound, radiant heat).
• Physiologic effects: Thermal energy (high temperature; heat) provides pain relief, increase in local blood flow, metabolism, and elasticity of connective tissues.² Heat increases blood flow and subsequently may induce edema and exacerbate acute inflammation.
• Indications: Heat is usually used for subacute to chronic conditions. It can reduce pain and muscle spasm, relax skeletal muscles, and decrease joint stiffness.
• Contraindications: patients with peripheral vascular disease, bleeding disorders, local malignancy, acute inflammation or trauma, edema, infection, open wounds, over large scars, patients with impaired sensation (neuropathy) or impaired ability to communicate/cognitive impairments (dementia or dysphasia).

Deep Heat

• Deep heat modalities include ultrasound, shortwave diathermy (SWD) and microwave diathermy (MWD). Ultrasound is however the most used deep heating agent. Heat penetration can be 3-5 cm or more without overheating underlying subcutaneous tissue or skin.
• Transfer method: Same as superficial heat but deeper penetration. The ultrasound machine converts electrical energy into acoustic energy via the piezoelectric effect. SWD and MWD convert electromagnetic energy to thermal energy.
• Physiologic effects: Same as superficial heat. The physiologic effects of ultrasound can be divided into thermal (heat) and non-thermal effects (cavitation, acoustic streaming, and standing waves). The non-thermal effects of ultrasound may improve repair of soft tissue injury, the inflammatory response, protein synthesis, and modulate membrane properties.⁴
• Indications: Ultrasound has been widely used in the treatment of various soft tissue disorders including bursitis, tendinitis, degenerative arthritis, adhesive capsulitis musculoskeletal pain, contractures, and promotes wound healing.⁵ SWD has good bone penetration, commonly used to heat large area of deep tissues and within the joints, such as hip, knee, or ankle. MWD has more superficial heat penetration compared to SWD and ultrasound. It is commonly used to heat superficial muscles and shallow joints.
• Contraindications: Besides the superficial heat contraindications listed above, specific ultrasound contraindications include use over the eyes, pregnant uterus, malignant area, near the heart, brain or spine, laminectomy sites, epiphyseal plates of children and patients with pacemakers. Ultrasound precautions include metal plates, screws, pins, external fixators, and joint replacement components. SWD and MWD contraindications: metal items, contact lenses, gravid or menstruating uterus, and skeletal immaturity. MWD increases the chance of miscarriages among pregnant therapists.⁴

Cryotherapy

• Common cold modalities include cold packs, ice massage, cold baths, vapocoolant sprays, and cold compression units. These modalities lower local tissue temperature.
• Transfer method: Cold occurs when hot objects/areas lose heat to cold objects/areas through the Second Law of Thermodynamics and entropy. Cold therapies lower and maintain a lower temperature either physically and/or chemically. Depth of cold penetration depends on the intensity and duration of application. At least 15 minutes is necessary to achieve an analgesia effect, and 20 minutes is the usually recommended treatment duration.⁵ Treatment time for ice massage is usually 7-10 minutes.
• Physiologic effects: Cold energy (low temperature) decreases pain, blood flow, edema, inflammation, muscle spasm, and metabolic demand of tissues.² Physiologic effects works via the Lewis hunting reaction or hunting response (or hunting reflex) where there is an alternating vasodilating (initial 5 minutes and >15 minutes; decreases sympathetic neurotransmitters to arteriovenous anastomosis, which then increases blood flow and temperature) and vasoconstricting response to application of cold.⁶ Vapocoolant sprays such as Fluori-Methane spray produce abrupt temperature changes over a small surface area. The spray can stimulate Aβ fibers to reduce pain and decrease muscle spasm.
• Indications: Acute inflammation and edema, spasticity, pain, arthritis, bursitis, muscle strain and ligament sprain, muscle spasm, and myofascial trigger points.
• Contraindications: Hypersensitivity or poor tolerance to cold, Raynaud’s disease/ phenomenon, peripheral vascular disease, open wounds, burns, cryoglobulinemia, paroxysmal cold hemoglobinuria, patients with impaired sensation (neuropathy) or impaired ability to communicate/cognitive impairments (dementia or dysphasia).

Relevance To Clinical Practice/Specific Techniques

Hot packs

• Provide superficial heat.
• Most common ones sold in the market are pre-packaged.
• Package inside contains chemicals needed to create thermal energy.
• Crushing or squeezing the contents in the package activates ingredients (which may be made of magnesium and water or iron, carbon, water, and a salt mixture).
• Some hot packs are gel based (and reusable in boiling water for 10-15 minutes) or require addition of hot water (in a bottle).
• Technique: Wrap a towel over the hot pack and then place over the affected area.
• Treatment duration is about 15 to 20 minutes.
• Commonly used for soft tissue pains, muscle spasms, strains/sprains, and osteoarthritis.
• Precautions: Avoid skin atrophy, burns, open wounds, rashes, cardiovascular disease, hypertension, or malignancy.

Heating pads

• Provide superficial heat.
• Most heating pads come in electrical and microwavable forms.
• Many of the heating pads are wearable with different sizes and shapes (i.e., for shoulder, back, feet, or full body blanket or mattress).
• Some electrical heating pads include a moist/damp setting with ability to control temperature settings.
• Others have a weighted fabric component for helping with insomnia and pain.
• Technique: Place the heating pad over the affected area.
• Treatment duration is about 15 to 20 minutes.
• Commonly used for soft tissue pains, muscle spasms, strains/sprains, osteoarthritis, and menstrual cramps.
• Precautions: Avoid skin atrophy, burns, open wounds, rashes, cardiovascular disease, hypertension, or malignancy.

Paraffin bath

• This is a machine unit which uses paraffin wax (or a combination of wax/oil) covered over the extremity of interest to deliver superficial moisturizing heat.
• Paraffin wax and mineral oil mix is in a 7:1 or 6:1 ratio.
• Treatment temperature is between 52.5 °C to 54.4 °C.
• Techniques:
  • Dipping: Dip body parts into a paraffin bath and then quickly remove to build coating of wax, repeat 7-12 times, followed by wrapping in wax paper or plastic bag, then cover with towels.
  • Immersion: Serial dips are followed by immersion in the paraffin bath for 30 minutes.
  • Brushing: A brush is used to apply paraffin to large body parts.
• Treatment duration is about 20 -30 minutes.
• Commonly used to heat irregular surfaces such as hands and feet, rheumatoid arthritis, osteoarthritis, trauma, contractures, and scleroderma.
• Paraffin bath with intrinsic muscle exercises has been shown to improve precision grip and pain in rheumatoid arthritis,⁷ provide short term relief of pain, improve function, and improve quality of life for symptomatic hand osteoarthritis,⁸ and is more effective when combined with mobilization techniques for post-traumatic stiff hand.⁹ Paraffin baths may have poor efficacy compared to lukewarm water in pretreating hands with scleroderma for hand mobility⁹ and may offer no additional benefits to home exercises.¹⁰
• Precautions: Avoid poor blood circulation, neuropathy, open wounds, and rashes; catching fire with paraffin wax; monitor temperatures from exceeding the treatment range.

Infrared (Radiant heat)

• An infrared lamp provides superficial dry heat to the body.
• Infrared lamps emit light energy which is absorbed through skin and converted to superficial heat with a depth of penetration <1 cm.
• Technique: Lamp is placed at a distance of about 20 inches away from the skin.
• Treatment duration is for about 20 minutes.
• Heating effectiveness decreases dramatically as the distance from body to lamp increases.
• Commonly used for patients who cannot tolerate the weight of hot packs.
• Precautions: Avoid burns, light sensitivity, skin drying, and use of photosensitizing medications.

Fluidotherapy

• This is a type of superficial dry heat which provides a desensitization effect by agitation of particles around the affected extremity.
• Temperature range is between 115 °F to 120 °F (46.7 °C to 48.9 °C).¹¹
• Technique: Hot air is blown through a container holding fine cellulose particles. Range of motion exercises are allowed during treatment.
• Treatment duration is about 20 minutes.
• Commonly used to heat hands, wrists, and arms to decrease pain, edema, and stiffness
• Fluidotherapy with conventional rehabilitation has been shown to be effective for neuropathic pain and reducing edema volume in subacute stage of poststroke CRPS46 and improve activities of daily living.¹²
• Precautions: Avoid open or infected wounds, those with neuropathy, lymphatic obstructions, or vascular diseases (ulcers).

Shortwave diathermy (SWD)

• Machine which converts high frequency alternating electromagnetic current (AC; aka. alternating current; radio waves) to thermal energy (friction) to provide deep heat to large areas of therapeutic interest.
• Used when therapeutic US is unable to heat deeper tissue structures.
• SWD units can use either capacitor or inducer cable electrodes.
• Frequency: Most commonly used is 27.12 MHz.
• Technique: Capacitor electrodes are placed opposite one another to induce deep heat. If using cable electrodes, these are placed over a large area of interest (i.e., wrapped around leg or sitting on back) to induce deep heat.
• Treatment duration is 20-30 minutes for one body area.
• Commonly used and is effective for short term musculoskeletal pain relief and improving quality of life.¹³
• SWD was shown to be effective in reducing pain in knee osteoarthritis and improving functionality but there was no significant difference in results whether it was pulsed or continuous setting.¹⁴
• Precautions: Avoid burns, skeletal immaturity (children with long bone growth plates), metal implants, stimulators, or any organs with excess fluid involvement, such as edematous skin, eyes, or uterus (pregnant/gravid).

Microwave diathermy (MWD)

• Machine which converts electromagnetic microwaves to thermal energy to provide deep heat.
• More superficial heat penetration compared to US and SWD: 1-4 cm
• Frequency: 915 to 2,456 MHz.
• Technique: Similar to SWD. Capacitor electrodes are placed opposite one another to induce deep heat. If using cable electrodes, these are placed over a large area of interest (i.e., wrapped around leg or sitting on back) to induce deep heat.
• Treatment duration is 5-15 minutes.
• Commonly used for superficial muscles and shallow joints.
• Precautions: same as SWD. Anyone who is near the machine and pregnant should exercise increased caution (e.g., operator, patient, clinician).

Cold packs

• Use of commercial cold or ice packs to provide cold therapy (lowering temperature) through the Hunting reflex (alternating vasodilation/vasoconstriction).
• Traditionally, cold packs provide analgesic effects by vasoconstriction and preventing inflammatory cells from flooding the site of injury.
• Immediate use of cold packs can help reduce symptomatic pain and swelling. However, cold packs should not be used for an elongated period of time (more than 20 minutes at a time) so that it does not delay healing or cause further damage.
• Technique: Cover with towel and do not let skin come in direct contact with cold packs.
• Treatment duration is 15-20 minutes. Onset of numbness is around 20 minutes.
• Commonly used for acute musculoskeletal pains, swelling, bruising, inflammation, and strains/sprains.
• Precautions: Avoid burns, skin hypersensitivity/poor tolerance to cold, those with neuropathy, Raynaud’s phenomenon, peripheral vascular diseases/conditions, open wounds, and cryoglobulinemia.

Ice massage

• Combination of ice and massage to provide cold therapy (lowering temperature) through the Hunting reflex (alternating vasodilation/vasoconstriction) and mechanical deformation of forces around the tissues. Similar pathophysiology to cold packs.
• Technique: use of ice (in a cup) over small areas by using gentle stroking motions.
• Treatment duration is 7-10 minutes; up to 15 minutes.¹⁵
• Commonly used for acute musculoskeletal pains, swelling, bruising, inflammation, and strains/sprains. May also be used to initiate and facilitate swallowing in stroke patients.¹⁶
• Precautions: Avoid burns, skin hypersensitivity/poor tolerance to cold, those with neuropathy, Raynaud’s phenomenon, peripheral vascular diseases/conditions, open wounds, and cryoglobulinemia.

Vapocoolant sprays (Freeze or cold sprays)

• Commercially available aerosol spray with liquefied chemical ingredients (chloroethane, tetrafluoroethane, or dimethyl ether) to provide topical cold anesthetic.
• Technique: “Spray-and-stretch” is commonly used. Apply the spray in one direction parallel to muscle fibers at a rate of 4 inches/sec while the muscle is passively stretched.
• Treatment duration is 30 to 60 seconds.
• Commonly used before local musculoskeletal injections.
• Precautions: Avoid skin irritation and local freezing.

Cold compression units

• Machine which uses circulating cold water attached to an intermittent pump unit to provide pneumatic compression to provide cold therapy.
• Comes in two forms of wearable compressions: static or dynamic.
• Settings:
  • Temperature: 45°F (7.2°C).
  • Pressure: Up to 60 mmHg.
• Technique: Static compression units are worn on the affected area with simple graded pressure. Dynamic compression units allow the user to have more control over compression pressure (and temperature) over affected areas and are used by healthcare professionals and providers.
• Treatment duration should be 15-20 minutes on and off.
• Commonly used to treat acute musculoskeletal injury with soft tissue swelling or used after surgical procedures.
• Precautions: Avoid in those with history of hypercoagulability, deep vein thrombosis, thrombophlebitis, skin hypersensitivity/poor tolerance to cold, those with neuropathy, Raynaud’s phenomenon, peripheral vascular diseases/conditions, open wounds, and cryoglobulinemia.

Ultraviolet (UV) therapy¹⁷

• UV light is electromagnetic radiation with high energy.
• There are three types – A, B, C. Type A is safest. The depth of penetration is determined by its wavelength/frequency.
• Technique: There is no standard treatment protocol. The UV light is directed at a body part to render treatment. Administered in small doses.
• Treatment duration is variable depending on condition. Ranges from 2 to 20 minutes.
• Commonly used for stimulating collagen metabolism, wound healing, and localized pain control. Types A and B are used for many skin disorders. Type C is not used as it sterilizes and penetrates and damages the body.
• Precautions: Burns (UV type B), cataracts/retinal damage (UV type A), skin cancer (melanoma), inflammation, and acceleration of skin aging. Caution with medications (e.g., fluoroquinolones, furosemide, TMP/SMX, diphenhydramine, oral contraceptive pills, tretinoin, isotretinoin) which increases risk for burns with UV.

Temp low-level laser therapy (LLLT)¹⁸

• LLLT delivers minimal energies (between 1 and 4 Joules).
• The depth of penetration is determined by its wavelength/frequency.
• Technique: There is no standard treatment protocol. The laser probe is applied perpendicular to the targeted treatment area.
• Treatment duration is about 30 to 60 seconds.
• Commonly used for stimulating collagen metabolism, wound healing, and localized pain control.
• Precautions: Seizures, epilepsy, malignancy, irradiated neck region in hyperhidrosis, exposed retina, and pregnant exposed abdomen.

Gaps in Knowledge/Evidence Base

N/A

Cutting Edge/Unique Concepts/Emerging Issues

Low-Level Laser Light Therapy (LLLT) is a relatively new therapeutic modality. LLLT received FDA approval in 2002 for the treatment of pain associated with carpal tunnel syndrome and in 2004 for iliotibial band syndrome. Most studies have focused on pain management and wound healing. Recently, the effects of LLLT on nerve tissue have been investigated.^19,20 However, the literature on LLLT effectiveness is conflicting. More research is needed to further investigate its effectiveness and to determine optimal treatment parameters.

Infrared therapy is another novel therapy in regenerative medicine. In one clinical randomized control trial by Sangma et al., infrared heat with routine dressing was more effective in reducing ulcer size and healing for chronic diabetic foot ulcers.²¹ Newer studies reveal infrared neural stimulation (INS) can help with wound healing and nerve tissue regeneration due to photothermal effects and can be combined with transcranial direct current brain stimulation for inducing neural stimulation and regeneration in traumatic brain injury.²²

References

1. Fischer E, Solomon S. Physiological responses to heat and cold. In: Licht S, ed. Therapeutic Heat and Cold. 2nd Revised ed. New Haven: E. Licht; 1965:126-169.
2. Campbell EA, Hynynen J, Burger B, Vainionpää A, Ala-Ruona E. Vibroacoustic treatment to improve functioning and ability to work: a multidisciplinary approach to chronic pain rehabilitation [published online ahead of print, 2019 Nov 13]. Disabil Rehabil. 2019;1-16. doi:10.1080/09638288.2019.1687763
3. Chen WS, Annaswamy TM, Yang W, Wang TG. Physical Agent Modalities. In: Cifu DX et al., eds. Braddom’s Physical Medicine & Rehabilitation. 5th ed. Elsevier; 2016.
4. Dyson M. Role of ultrasound in wound healing. In: McCullough JM, Kloth L, Feedar JA, eds. Wound Healing: Alternatives in Management. 2nd ed. Philadelphia, PA: F.A. Davis Company; 1995:318-345.
5. Ouellet-Hellstrom R, Stewart WF. Miscarriages among female physical therapists who report using radio- and microwave-frequency electromagnetic radiation. American journal of epidemiology. 1993;138(10):775-786.
6. Chen WS, Annaswamy TM, Yang W, Wang TG. Physical Agent Modalities. In: Cifu DX et al., eds. Braddom’s Physical Medicine & Rehabilitation. 5th ed. Elsevier; 2016.
7. Iswarya S, Begham A, Govind S, Singh K. A study on the effectiveness of paraffin wax bath therapy and intrinsic muscle exercises in reducing pain and increasing precision gripping movements of rheumatoid hand. Journal of Pharmaceutical Sciences and Research. 2018;10(10):2686-2688.
8. Kasapoğlu Aksoy M, Altan L. Short-term efficacy of paraffin therapy and home-based exercise programs in the treatment of symptomatic hand osteoarthritis. Turk J Phys Med Rehabil. 2017;64(2):108-113. Published 2017 Oct 2. doi:10.5606/tftrd.2018.1535
9. Sibtain F, Khan A, Shakil-Ur-Rehman S. Efficacy of Paraffin Wax Bath with and without Joint Mobilization Techniques in Rehabilitation of post-Traumatic stiff hand. Pak J Med Sci. 2013;29(2):647-650.
10. Kristensen LQ, Oestergaard LG, Bovbjerg K, Rolving N, Søndergaard K. Use of paraffin instead of lukewarm water prior to hand exercises had no additional effect on hand mobility in patients with systemic sclerosis: A randomized clinical trial. Hand Therapy. 2019;24(1):13-21. doi:10.1177/1758998318824346
11. Schandelmaier S, Kaushal A, Lytvyn L, et al. Low intensity pulsed ultrasound for bone healing: systematic review of randomized controlled trials. BMJ. 2017;356:j656. Published 2017 Feb 22. doi:10.1136/bmj.j656
12. Sezgin Ozcan D, Tatli HU, Polat CS, Oken O, Koseoglu BF. The Effectiveness of Fluidotherapy in Poststroke Complex Regional Pain Syndrome: A Randomized Controlled Study. J Stroke Cerebrovasc Dis. 2019;28(6):1578-1585. doi:10.1016/j.jstrokecerebrovasdis.2019.03.002
13. Boonhong J, Thienkul W. Effectiveness of Phonophoresis Treatment in Carpal Tunnel Syndrome: A Randomized Double-blind, Controlled Trial. PM R. 2020;12(1):8-15. doi:10.1002/pmrj.12171
14. Masiero S, Pignataro A, Piran G, et al. Short-wave diathermy in the clinical management of musculoskeletal disorders: a pilot observational study. Int J Biometeorol. 2020:64;981–988. https://doi.org/10.1007/s00484-019-01806-x
15. Nakamura T, Fujishima I. Usefulness of ice massage in triggering the swallow reflex. J Stroke Cerebrovasc Dis. 2013;22(4):378-382. doi:10.1016/j.jstrokecerebrovasdis.2011.09.016
16. Crevenna R, Mickel M, Keilani M. Extracorporeal shock wave therapy in the supportive care and rehabilitation of cancer patients. Support Care Cancer. 2019;27(11):4039-4041. doi:10.1007/s00520-019-05046-y
17. Raikes AC, Killgore WD. Potential for the development of light therapies in mild traumatic brain injury. Concussion. 2018;3(3):CNC57. Published 2018 Oct 15. doi:10.2217/cnc-2018-0006
18. Navratil L, Kymplova J. Contraindications in noninvasive laser therapy: truth and fiction. Journal of clinical laser medicine & surgery. 2002;20(6):341-343.
19. Hashmi JT, Huang YY, Osmani BZ, Sharma SK, Naeser MA, Hamblin MR. Role of low-level laser therapy in neurorehabilitation. PM & R: the journal of injury, function, and rehabilitation. 2010;2(12 Suppl 2):S292-305.
20. Rochkind S. The role of laser phototherapy in nerve tissue regeneration and repair: research development with perspective for clinical application. Proceedings of the World Association of Laser Therapy; 2004; Sao Paolo, Brazil.
21. Freire B, Geremia J, Baroni BM, Vaz MA. Effects of cryotherapy methods on circulatory, metabolic, inflammatory and neural properties: a systematic review. Fisioterapia em Movimento. 2016;29(2):389-398. https://doi.org/10.1590/0103-5150.029.002.AO18
22. Sangma M, Selvaraju S, Marak F, Dasiah S. Efficacy of low level infrared light therapy on wound healing in patients with chronic diabetic foot ulcers: a randomised control trial. International Surgery Journal. 2019;6(5):1650-1653. doi:http://dx.doi.org/10.18203/2349-2902.isj20191885

Original Version of the Topic

Thiru M. Annaswamy, MD, Li Liu, MD. Therapeutic Modalities. 4/4/2016

Previous Revision(s) of the Topic

Benjamin J. Seidel, DO, Lawrence Chang, DO, MPH, Aaron Greenberg, DO. Therapeutic Modalities. 3/11/2021

Author Disclosure

Charnette Lercara, MD
Nothing to Disclose

Lon Yin Chan, MD
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Elver Ho, MD
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Supriya Baskaran, BS
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Ahmed Elzayat, BA
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