Modalities are physical agents used to produce a therapeutic change in tissue.¹ These agents are typically used in conjunction with a comprehensive treatment plan. Their use starts with a modality prescription (Table 76–1). The prescription is then utilized to follow through with the application of the specific modalities. This chapter will discuss those modalities, physiology, applications, and evidence for their use.

Heat Transfer and Physiology

There are a number of modes of heat therapy that are currently used in practice. They include types of superficial and deep heating. The superficial types most commonly utilized are heating pads, heating packs, fluidotherapy, and paraffin baths. Deep heating modalities include ultrasound, shortwave diathermy, and microwave diathermy.

Heat transfer occurs through one of the following processes:

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  Conduction: Between 2 bodies in contact

  
  
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  Convection: Through a medium (air, water, blood)

  
  
• 
  

  Evaporation: Transferred from a liquid to a gas

  
  
• 
  

  Radiation: Emitted from a body with a surface temperature above zero

  
  
• 
  

  Conversion: Transformation of electromagnetic or sound energy into thermal energy

Physiologically, heat produces therapeutic benefits on the body through various effects. Heat causes vasodilatation on the arterioles and venous systems allowing increased blood flow to and from an injury site. Nerve conduction velocity is seen to modestly increase, which may aid in proprioception retraining after an injury. Muscle and tendon extensibility has been shown to increase as well as an improvement in joint stiffness. Finally, analgesia is experienced through thermotherapy.¹ General indications are discussed in the text and contraindications are listed in Table 76–2.

Superficial Heat

Superficial heat involves the transfer of thermal energy to the patient from a device or object. Examples include heating pads, hot packs, paraffin baths, and fluidotherapy (whirlpools). Importantly, these mechanisms can heat structures no more than 2 cm deep, therefore, utilization for deeper structures will not be effective. Contraindications to superficial heat include edema and malignancy (see Table 76–3).

Heating Pads

Heating pads are commonly found in homes and are readily available commercially. Heating pads work by means of conduction. The heating pad’s energy source is either electric or by circulating fluid.¹ This conductive heat is useful in heating superficial tissue which is less than 1 cm deep. Precautions should always be maintained with heating modalities regarding the potential for burns, especially in those with prominent boney landmarks.¹ These units should also be routinely inspected, due to the potential for electric shock.¹ Repetitive use of either heating pads or hydrocollator pack pads can lead to permanent skin dislocation, referred to as erythema ab igne³ (see Fig. 76–1)

Hot Packs

Hot packs are another heating modality that are commonly utilized especially in an ambulatory therapy setting for the management of muscular spasm, strains, and osteoarthritis. The most common type of hot packs are hydrocollator packs. These packs are made up of silicon encased in a canvas sack. They are put in a unit filled with water that has been heated to 166°F.¹ These packs can then be removed from the water and wrapped in towels or manufactured hydrocollator pads that diffuse the direct heat from touching the surface of the intended treatment area. Treatment times in practice vary from 15 to 30 minutes. It is critical to protect the patient from direct exposure.

Research has shown an elevation of tissue temperatures to 1°F to 3°F at depths of 1 to 2 cm.^4,5 Heat packs have reportedly been most effective for tissue elevation of skin and adipose tissue.⁶ They have also been shown to have a clear effect on shoulder range of motion.⁶ Studies looking at the effect of heating and stretching have shown that there are significant increases in range of motion compared to stretching alone.⁶

Fluidotherapy

Fluidotherapy utilizes convection as a means for heat transfer. The units are typically designed for upper or lower extremity treatments. The extremity that is being treated is placed in a dry heat environment that has circulating cellulose particles providing tactile stimulation, which prevents pain in the high heat environment.⁷ This phenomenon of a solid–gas system that behaves much like boiling liquid is termed “fluidization,” which is where this therapy received its name.⁸

Studies have shown that fluidotherapy does significantly elevate tissue temperature after a 20-minute treatment.^7,9,10 It has also been shown that distal sensory nerve latencies decrease with fluidotherapy, which may provide a theory for pain modulation.¹⁰

Current practice utilizes this therapy for the heating modality as well as the ability to perform active range of motion exercise during the treatment.¹¹ Common indications include osteoarthritis, postoperative stiffness, sprains, and strains. There are also case reports of successful use of the modality in the treatment of complex regional pain syndrome.¹² Clinical outcome studies are lacking.

Paraffin Baths

Paraffin baths are a combination of paraffin wax and mineral oil that are mixed to ratios between 6:1 and 7:1.¹ This type of heat therapy uses conduction as its mode of heat transfer; paraffin has a low heat capacity and, therefore, facilitates better tissue heat tolerance. The wax is heated to temperatures between 45°C and 54°C. Although subcutaneous tissues may rise in temperature up to 5°C, intramuscular temperatures generally rise by only 1°C. The extremity that is being treated is then dipped into the wax bath and removed, which creates an insulating layer of wax on the outside of the extremity. The insulating layer of wax protects the extremity from the higher temperatures of the wax.

Paraffin baths were first studied in the 1960s, when it was shown that the paraffin immersion method produced elevation in tissue temperatures greater than multiple other heating modalities.⁵ More recently, the therapeutic benefits of paraffin baths were shown in clinical trials that studied patients with rheumatoid arthritis, osteoarthritis, and scleroderma.^13–15 A Cochrane review concluded that paraffin baths in conjunction with exercise can be beneficial for short-term relief in patients with arthritic hands.¹⁶ Finally, it has also been shown to be beneficial in conjunction with exercise in post-traumatic stiffness of the hands and ankles.^17,18 Inexpensive, commercially available units are widely available for home use.

Ultrasound

Ultrasound is acoustic vibrations or sound at frequencies that are not audible. Ultrasound is used for diagnostic and therapeutic reasons in medicine. Therapists often utilize high-frequency ultrasound (>20 kHz) through a medium (gel or water) to heat deep structures. Ultrasound parameters are changed to produce images in diagnostic ultrasound and thermal effects in therapeutic ultrasound. It works through the reverse piezoelectric effect in which an electric current passes across a crystal producing the acoustic waves. When these acoustic waves are absorbed in tissue, it is thought to cause molecular vibration, which in turn causes the thermal effects.¹ Great care should be taken to avoid heating certain structures, including the heart, brain, and the gravid uterus (see Table 76–4).

There are adjustable parameters for therapeutic ultrasound, depending on the goal of therapy (see Table 76–5). Frequencies between 1 and 3 MHz are common settings for either deep heating (1 MHz) or superficial heating (3 MHz). Intensity is adjusted to change the amount of power that is directed to a specific surface area and is expressed in watts per centimeters squared (W/cm²). Ultrasound can be continuous or pulsed. Clinically, it is felt that pulsed ultrasound can be used for nonthermal effects of ultrasound. Pulsed ultrasound settings include the duty cycle which is the percentage of time that the pulses are occurring expressed as a percentage of time (50%). Pulse duration and frequencies can also be set. Finally, the duration of treatment is set, which commonly is 5 to 10 minutes.¹

Ultrasound therapy is a very common modality used in therapy settings. In a British survey, 84% of physiotherapists utilized ultrasound.¹⁹ Despite its popularity, most of the research has been in vitro and a review from the American Physical Therapy Association stated that there was very little evidence of the effects of ultrasound with in vivo research.²⁰ Multiple reviews have concluded that research is lacking and there is little evidence to support ultrasound therapy in the treatment of musculoskeletal disorders.^21,22 Multiple Cochrane reviews have shown little or no benefit for therapeutic ultrasound in chronic low back pain, carpal tunnel, acute fractures, and acute ankle sprains.^23–26 On the other hand, recent reviews regarding rheumatoid and osteoarthritis have shown a benefit for hand strength, decreasing pain, and increased functional scores after therapeutic ultrasound.^27–29 The Philadelphia panel also found that there is good evidence for continuous therapeutic ultrasound for short-term pain relief in calcific tendonitis.³⁰ Continued research in this area with controlled clinical trials is needed. Ultrasound may produce rapid heating of methyl methacrylate or high-density polyethylene used in some total arthroplasties, and some have cautioned against its use in this situation.³¹

Phonophoresis

Phonophoresis is defined as the use of ultrasound to deliver therapeutic drugs to or through the skin. It has been hypothesized that drugs are able to be delivered by a process of acoustic cavitation. This is the process by which liquid is pulled apart when it is acted upon by a force in excess of its tensile strength, causing the formation of voids in the system.³² This void is felt to be the mechanism by which a drug can enter and then be transported to the target tissue. Due to concerns regarding the current available research and inconclusive clinical outcomes, phonophoresis in clinical practice has become less popular.³³

Shortwave Diathermy

Shortwave diathermy refers to electromagnetic energy that, through conversion, is changed to thermal energy.¹ The electromagnetic energy comes in the form of radiofrequency waves typically with a frequency of 13.56 to 40.68 MHz as regulated by the federal communications commission.¹ Most units are developed with a single generator and amplifier set to produce one frequency capable of thermal effects³⁴ (see Fig. 76–2). The radiofrequency is then sent through a transformer, which converts the electromagnetic energy to be dispersed with an applicator.³⁴ The effects in the tissue are then produced by an oscillating electromagnetic field that leads to rapid ion movement and real flow of current in the tissue.³⁴ The end thermal effects are dependent on the electrical properties of the specific tissues being treated.

Significant changes in tissue temperature have been demonstrated to depths of 1 to 3 cm.^35–37 The thermal effects of shortwave diathermy have also been measured to cause increased active musculoskeletal compliance and a physiological decrease in muscle stiffness.³⁷ A review of thermotherapy shortwave diathermy found that it produced the greatest effect with heating and stretching compared to other modalities.⁶ This was also demonstrated in patients with adhesive capsulitis who had significantly better shoulder score index and improved range of motion compared to those receiving superficial heat or control.³⁸ A similar study looked at gastrocnemius heating and improvement of range of motion at the ankle showing significant increases compared to superficial heat or control.³⁹ Treatment times needed to produce these changes have been recorded at 15 to 30 minutes.^35–39

There has been some concern regarding exposure to electromagnetic radiofrequency fields, although no adverse health effects have yet to be established.⁴⁰ Other concerns would be the chance of serious burns from the unit.³⁴ It has been suggested that therapists should integrate their knowledge of anatomy, output intensity, electrode placement relative to tissues being treated, and communication with their patient for reduction of harm from this treatment.³⁴ It has also been recommended that the patient be positioned on a nonmetallic couch or chair with the removal of any metal objects in the vicinity of the shortwave unit.⁴⁰

Microwave Diathermy

Microwave diathermy is another form of electromagnetic energy that is converted from radiofrequencies to thermal energy. This energy has been studied at frequencies of 915 MHz and 2450 MHz and has been shown to have thermal effects in tissue at 1 to 4 cm.⁴¹ On average, temperatures may reach roughly 41°C. Depth of tissue changes and frequencies administrated would be the main differences between shortwave and microwave diathermy. Duration of treatment generally lasts between 5 and 10 minutes, three times a week. Patients must wear protective eyewear. Few clinical trials have been performed, but one positive trial in patients with osteoarthritis showed significant improvement of pain, stiffness, strength, and physical function that was maintained over a 12-month period.⁴² Contraindications for shortwave and microwave diathermy are listed in Table 76–6.

Cryotherapy

Cryotherapy is the therapeutic application of any cooling agent to the body to remove heat with resultant decreased tissue temperature.⁴³ Its application is to help control pain, edema, and inflammation as well as the reduction of spasticity.⁴⁴ Common types of application include cold packs, ice massage, cryotherapy compression units, and cold-water immersion. General contraindications for the use of cryotherapy include cryopathies such as cryoglobulinemia, paroxysmal cold hemoglobinuria, Raynaud’s disease or phenomenon, and cold hypersensitivity, arterial insufficiency, impaired sensation, or simple cold intolerance⁴⁴ (see Table 76–7 for contraindications).

Although very commonly utilized, most of the research on cryotherapy use has examined the basic science-related physiologic effects of vasoconstriction, slowing of nerve conduction velocity, moderation of inflammation, suppression of metabolic activity, and delayed reactive vasodilatation, but little data is available on clinical results to help guide the practitioner. One study on ankle sprains concluded that the use of cryotherapy and compression resulted in greater improvements in swelling and the ability to bear weight than compression alone,⁴⁵ but a Cochrane review on the use of superficial cooling for low back pain was unable to draw any conclusions.⁴⁶ In athletic medicine, cold water immersion is used after workouts or games to assist with muscle recovery or delayed onset of muscle soreness, and there is some evidence it may be effective in this regard.^47–49

Reports of adverse effects include nerve palsies after application over the site of superficially located nerves, specifically the ulnar and peroneal nerves,^50–52 and frostbite.^53,54

Hydrotherapy

Hydrotherapy is the application of hot or cold water, frequently by immersion, for the treatment of disease. While hydrotherapy has traditionally been a commonly used modality, it is now infrequently utilized for a variety of reasons including space constraints, expense, concerns for transmitting infection, and time-consuming maintenance. It is still used in athletic medicine with contrast baths and as discussed under cryotherapy and heat therapy. Additionally, it may still be used in burn rehabilitation, please see Chapter 87, Burn Rehabilitation, for further discussion.

Electrotherapy

There have been multiple versions of electrotherapy in use since its development as a therapeutic modality. Machines in use today generally have a variety of modes and waveforms available for use in a single unit such as interferential, bi-phasic, high volt, Russian stimulation, microcurrent, and transcutaneous electrical nerve stimulation (TENS). TENS should be contrasted with functional neuromuscular stimulation (FNS), also referred to neuromuscular electrical stimulation. With FNS, electrical current is utilized to stimulate movement in a paretic or hemiparetic limb. The discussion will be limited to the most common types currently used and those with some evidence of efficacy. There are some general contraindications for all types of electrical modalities including use over the heart, carotid sinuses, anterior cervical region, gravid uterus, application over a region of active infection, malignancy, thrombophlebitis, simultaneous use with diathermy, and use in a patient with an implanted electrical device such as a cardiac pacemaker, defibrillator, spinal cord stimulator, or intrathecal pump.^55,56 These contraindications do not appear to be related to actual cases of injury, but rather recommendations based on theoretical risks. While generally considered safe, minor localized skin reactions including burns, skin irritation, blisters, rashes, bruising, swelling, and increased pain have been reported as adverse effects to electrical stimulation therapies.^54,57

Transcutaneous Electrical Nerve Stimulation (TENS)

TENS is the application of electrical stimulation to the skin for the purposes of pain control.⁵⁸ TENS was developed based on the gate control theory of pain. It is purported to reduce pain by stimulation of large diameter A-Beta primary sensory afferents, which in turn activate inhibitory interneurons in the substantia gelatinosa of the spinal cord thereby attenuating the transmission of nociceptive signals from smaller diameter A-delta and C fibers.⁵⁹ It has the advantage of being available in small, portable units which can be worn throughout the day. TENS may use high or low frequencies. High frequency has been defined as between 40 and 150 Hz,^59,60 and typically uses a pulse width of 50 and 100 µsec to stimulate sensory fibers.⁶⁰ Low frequency, also known as acupuncture-like TENS, has been defined as between 0.5 and 10 Hz with a pulse width of >150 µsec used at a higher intensity to stimulate both motor and sensory fibers.⁶⁰ In addition to differences in frequency, variations can also be made in amplitude, pulse width, and waveform.⁵⁹ Other modes described include brief intense TENS (> 80 Hz, >150 µsec), burst TENS (bursts of pulses delivered at low frequencies < 10 Hz), and modulation TENS (one or more stimulation parameters are randomly modulated during therapy).⁵⁹ These multiple modes may have value as some have concluded that response to different stimulation settings may vary significantly among individuals.^61,62

A systemic review of a variety of modalities in the treatment of chronic low back pain concluded that use of either high or low frequency TENS may have an immediate impact on pain reduction, but did not appear to improve pain in long term or improve perceived disability.⁵⁶ The results in chronic low back pain seem to be slightly better for high frequency TENS than low frequency.⁵⁶

A Cochrane review on the use of electrotherapy in neck pain was unable to draw firm conclusions on the use of TENS due to the poor quality of most of the reviewed studies. In both acute and chronic neck pain, it appears TENS may provide mild pain relief, probably producing a similar response as manual or ultrasound therapy, but not as good as exercise therapy.⁶³

While a Cochrane review was unable to draw any conclusions on the efficacy of TENS in the treatment of knee osteoarthritis,⁶⁰ a separate meta-analysis concluded that use of TENS did provide clinically relevant pain relief in the short term.⁶⁴ A subsequent randomized controlled trial, which compared the addition of either real or sham interferential therapy, TENS, or shortwave diathermy to exercise therapy in the treatment of knee osteoarthritis did not result in any significant pain reduction. However, there was a significant decrease in analgesic medications in the treatment groups receiving one of the real modalities, suggesting they may indeed provide some pain relief.⁶⁵ There did not appear to be any significant differences in the response to the various modalities, suggesting one may be as effective as another.⁶⁵ Contraindications for TENS therapy are listed in Table 76–8.

Interferential Current Therapy (IFC)

Traditional IFC is applied with two sets of electrodes and four electrical pads using two out of phase frequencies, typically one at 4000 Hz and the other at 4100 Hz, which “interfere” within the tissue producing a lower frequency current, with the goal of producing an analgesic effect.^60,66 Modulated IFC only uses two electrical pads with directed current, which vectorially sums in the tissue, with typical settings of 4000 Hz for the carrier frequency, a beat frequency of 80 Hz, and a modulation frequency between 0 and 150 Hz.⁶⁰ Proposed mechanisms for the analgesic effects of IFC include the gate control theory of pain, descending pain suppression, block of nerve conduction, increased circulation, and even a placebo effect.⁵⁵