Common Therapeutic Modalities in Animal Rehabilitation

Common Therapeutic Modalities in Animal Rehabilitation

Part I

Ronald B. Koh* and Janice Huntingford

* Corresponding author


The use of therapeutic modalities, also known as electrophysical agents, is widespread in the field of veterinary medicine including physical rehabilitation, sports medicine, integrative medicine, pain medicine, geriatric medicine, and palliative and hospice medicine. They are noninvasive therapies used to complement other therapeutic interventions and together lead to optimal therapeutic outcomes for patients. Therapeutic modalities are essential components of a complete rehabilitation program in veterinary medicine to assist in controlling pain and inflammation, and regaining joint range of motion, flexibility, muscular strength, and balance, thus enhancing a full functional recovery. In general, therapeutic modalities can be categorized as thermal, mechanical, or electromagnetic. Thermal agents include thermotherapy and cryotherapy agents. Mechanical agents include traction, compression, water, and soundwaves. Electromagnetic agents include electromagnetic fields, photobiomodulation, and electrical currents. Some therapeutic agents fall into more than one category. Water and ultrasound, for example, can have mechanical and thermal effects. This chapter with three parts focuses on the therapeutic modalities most commonly used in animal rehabilitation in the United States, including cryotherapy, thermotherapy, photobiomodulation, and electrical therapy. Part I focuses on the discussion of thermal energy modalities. Photobiomodulation and electrical therapy are discussed in Parts II and III respectively. The clinical application of these therapeutic interventions is based on their history of clinical use and research data supporting their efficacy. However, there is still a great need for high-quality, randomized, double-blinded placebo-controlled clinical studies to determine their therapeutic efficacy in veterinary patients.


Cryotherapy, the therapeutic use of cold, has clinical applications in rehabilitation. Cryotherapy is applied to the skin but can decrease tissue temperature deep to the area of application in order to control pain, decrease inflammation and edema, and reduce spasticity [1]. Animal models have demonstrated that tissue cooling can have significant beneficial effects on postoperative or post-injury pain, inflammation, and swelling by reducing or delaying infiltration of white blood cells and subsequent inflammatory cytokines within injured tissue [24].

The means by which cold or heat is delivered to the target tissue is attributed to the following physical mechanisms: conduction, convection, radiation, conversion, and evaporation [5]. Soft tissues such as adipose tissue, skeletal muscle, bone, and blood have different levels of thermal conductivity, therefore they do not conduct temperature changes in the same way [6]. Adipose tissue acts as insulation to underlying tissues limiting the degree of temperature change in deeper tissues. Blood and muscle contain relatively high-water contents, thus they readily absorb and conduct thermal energy or temperature changes.

Cryotherapy exerts its therapeutic effects by influencing hemodynamic, neuromuscular, and metabolic processes within the body [7].

  • Hemodynamic Effects: Cold applied to the tissue causes vasoconstriction, increased blood viscosity, and decreased capillary permeability resulting in reduction in blood flow [8]. Decreased blood flow impedes the movement of fluid from the capillaries to the interstitial tissue, thereby controlling bleeding, edema, and fluid loss after acute trauma or surgery. Cooling of the tissue also reduces inflammation and edema by decreasing the production and release of vasodilator mediators, such as histamine and prostaglandins, resulting in reduced vasodilation [9].
  • Neuromuscular Effects: The use of cold has a variety of effects on neuromuscular function, including decreasing nerve conduction velocity, elevating the pain threshold, altering muscle force generation, decreasing spasticity, and facilitating muscle contraction [7]. When tissue temperature is decreased, nerve conduction velocity decreases, thus increase the pain threshold and decrease the sensation of pain [10]. Along with decreased blood flow, these physiological changes lead to some therapeutic effects such as a reduction in pain and muscle spasm, and the prevention of edema. When applied appropriately, cryotherapy can temporarily decrease spasticity of muscles by decreasing gamma motor neuron activity and afferent spindle activity because of decreased muscle temperature [11].
  • Metabolic Effects: Cold decreases the rate of metabolic reactions in treated tissues, thereby decreases the rate of reactions related to the acute inflammatory process [12]. The cooling of the tissue also inhibits enzymatic effects related to inflammation, and minimizes the release of histamine, which reduces tissue inflammation and damage [13].

Indications of Cryotherapy

Knowledge of the physiological effects of cold helps to identify the benefits of the use of cryotherapy as an adjunctive treatment intervention in rehabilitation, such as managing edema, pain, and abnormal muscle tone, etc., that are related to mobility and function. The therapeutic effect of cryotherapy is believed to occur when tissue temperature reaches 59 to 66.2°F (15 to 19°C).

  • Inflammation Control: Cryotherapy can be used to control acute inflammation, thereby accelerating recovery from injury or surgery [7]. Application of cold slows the rate of chemical and metabolic reactions that occur during the acute inflammatory phase, as well as directly reduces the heat associated with inflammation by decreasing the temperature of the area to which it is applied.
  • Edema Reduction: The decrease in blood flow associated with vasoconstriction in cryotherapy prevents the accumulation of fluid and metabolites in the injured area, thus reducing edema. Cryotherapy in combination with compression have been reported to be more effective than compression alone for the management of edema [14].
  • Pain Reduction: Cryotherapy is commonly used to decrease pain. The mechanism is likely due to increased pain threshold and decreased pain sensation as a results of decreased nerve conduction velocity by cryotherapy [10].
  • Reduction of Muscle Spasticity: Several studies indicate that spasticity can be reduced by cryotherapy [15]. The reduction of spasticity may be a result of direct cooling of the muscle decreasing activities of gamma motor neurons and afferent spindles [11].

Applications of Cryotherapy

Cryotherapy can be applied in several ways: reusable ice packs, ice cubes wrapped in a towel, ice cups, cold compression devices, cold water-circulating blankets, cold immersion, vapocoolant sprays, or contrast baths. Selection of the type depends on the desired effects, depth of penetration desired, stage of tissue healing, treatment area, and treatment goals. In animal rehabilitation, cold packs are a simple and effective method for cooling tissue in patients. There are commercially available cold packs, as well as cold packs that can easily be made at home or in the clinic. Ice packs can be made using a plastic bag or towel and crushed ice or ice cubes. They may be applied either directly to the skin or can be used with a wet or dry interface. Water has a higher conductivity than air, therefore wet cryotherapy may work better than dry cryotherapy.

Cryotherapy is usually recommended during the acute inflammatory phase of healing (which is typically lasts 48 to 72 hours after injury or surgery) to avoid delaying tissue healing. Following surgery or injury, applying cryotherapy to the incision or surrounding injured area for 10 to 15 minutes every 4 to 12 hours daily for the first three days is recommended. In general, cryotherapy should be applied for no longer than 20 minutes and at least an hour apart between treatments to avoid further tissue damage. Although cryotherapy is a relatively safe intervention, its use is contraindicated in some circumstances, and it should be applied with caution in animals. If the patient’s condition is worsening or is not improving after two or three treatments, the treatment approach should be reevaluated and changed. Figure 14.1.1 shows a dog is receiving cryotherapy post radiation to reduce pain and edema in the left shoulder affected by osteosarcoma. Precautions and contraindications of cryotherapy are as follows:

Figure 14.1.1 A dog is receiving cryotherapy post radiation to reduce pain and edema in the left shoulder affected by osteosarcoma.

Precautions for the use of cryotherapy:

  • Very young and very old patients
  • Small animals or extremities
  • Poor temperature regulation
  • Over the superficial main branch of a nerve
  • Over an open wound
  • Poor sensation
  • Hypertension

Contraindications for the use of cryotherapy:

  • Hypothermia
  • Cold hypersensitivity (cold-induced urticaria reported in humans)
  • Cold intolerance
  • Over-regenerating peripheral nerves
  • Over an area with circulatory compromise or peripheral
  • Vascular disease


Thermotherapy or heat therapy is the application of heat sources or thermal agents over skin surface areas for heating superficial and deep soft tissues to increase blood flow, relieve pain, increase tissue elasticity, and promote healing in the injured area. Like cold, heat has therapeutic effects on pain, soft tissue extensibility, and wood healing because of its influence on hemodynamic, neuromuscular, and metabolic processes in the body [7]. Thermotherapy causes vasodilation which increases tissue oxygenation and transport of metabolites, and increases rate of enzymatic and biochemical reactions that may facilitate tissue healing [5]. The use of heat also alters tissue viscoelastic properties which results in increased soft tissue extensibility, decreased stiffness, and improved range of motion [5].

  • Hemodynamic Effects: Heat stimulates the cutaneous thermoreceptors that are connected to the cutaneous blood vessels, causing the release of bradykinin which relaxes the smooth muscle walls resulting in vasodilation [16]. Vasodilation increase the rate of blood flow to the treated area. The increased blood flow reduces edema and accelerates wound healing by improving perfusion of the wound and peri-wound tissue and increasing oxygen tension of the wound [17]. Increasing tissue temperature to therapeutic levels (104°F to 111.2°F; 40°C to 45°C) can facilitate the release of oxygen from the blood’s hemoglobin, thus improving tissue nutrition [18].
  • Neuromuscular Effects: Increased tissue temperature with thermotherapy increases nerve conduction velocity and decreases the conduction latency of sensory and motor nerves [19]. Both effects may contribute to the reduced pain perception. Thermotherapy has also been shown to reduce muscle spasm by affecting the nerve firing rate (frequency) [20]. Muscle relaxation occurs because of a decreased firing rate of the gamma efferents, thus lowering the threshold of the muscle spindles and increasing afferent activity. There is also a decrease in firing of the alpha motor neuron to the extrafusal muscle fiber, resulting in muscle relaxation and decrease in muscle tone [18, 21]. Lastly, several studies demonstrate that the application of thermotherapy can increase the pain threshold by activation of the spinal gating mechanism [22]. Heated tissues increase the activity of the cutaneous thermoreceptors which have an immediate inhibitory gating effect on the transmission of the sensation of pain at the spinal cord level.
  • Metabolic Effects: The heating of tissue increases the rate of enzymatic biological reactions when a tissue is heated from 102°F to 109°F (39°C to 43°C), with the reaction rate increasing by approximately 13% for every 1.0°C (1.8°F) increase in temperature [23]. The enzymatic activity rate decreases and the protein constituents of enzymes begin to denature at temperature of 45°C (113°F) [24]. Increased enzymatic activity can lead to increase in metabolic rate and oxygen uptake which may contribute to acceleration of tissue healing in conjunction with the increased rate of blood flow caused by thermotherapy [25]. The use of heat also stimulates fibroblast proliferation [26], accelerates endothelial cell proliferation [27], and improves phagocytic activity of inflammatory cells [28], thus promoting tissue healing after injury.

Indications of Thermotherapy

The main benefits of thermotherapy include pain relief, reduction of edema, decreased of muscle stiffness or spasm, and increased tissue flexibility. In animal rehabilitation, thermotherapy is commonly used as an adjunctive intervention technique to facilitate the accomplishment of the treatment goals.

  • Pain Reduction: Thermotherapy is well recognized for the alleviation or management of pain mainly through via the gate-control mechanism. Heat has also been shown to elevate the pain threshold, and increase nerve conduction velocity [22, 29].
  • Reduction of Muscle Guarding: Muscle guarding (muscle tonus) is a protective response in muscle after intensive exercise, injury, or trauma. However, intensive muscle guarding could lead to muscle spasms, stiffness, pain, and reduced range of motion. Thermotherapy relaxes muscle and improves the efficacy of stretching by reducing muscle tonus (guarding) through the reduction of gamma motor neuron excitability and muscle spindle sensitivity [30].
  • Increased Tissue Extensibility: Shortening of connective tissue is common in aging, injured, or immobilized animals, which may result in decreased range of motion and impaired function. Heat therapy has been shown to increase tissue extensibility and improve flexibility and range of motion in rehabilitation [31]. Heat increases viscoelastic properties of collagen in connective tissues, specifically muscle, tendon, and joint capsule, thus enhancing the efficacy of stretching, reducing muscle spasms, and alleviating pain [32]. Furthermore, the use of heat therapy before stretching reduces muscle irritation and spams to enhance tissue flexibility and range of motion. Stretching is best applied immediately after removal of the heat source.

Applications of Thermotherapy

Thermotherapy can be performed in the form of either superficial or deep (penetrating) heating agents. Common examples of superficial thermotherapy are heat packs, whirlpools, hot tubs and Jacuzzis, and paraffin baths, with heat packs being the most common thermotherapy used in animals. Heat can be induced in the deeper tissues through electrotherapy, including ultrasound, phonophoresis, and diathermy heat, with ultrasound being commonly used in animals. The selection of the appropriate heating agent is based on the size and location of the area to be treated, depth of affected tissue, and treatment goals. Cautions must be taken when using electric heating pads or infrared lamp on animals as they pose a higher risk of burns. Never place electric heating pads under anesthetized, immobilized, or paralyzed animals without close monitoring.

There are also two different types of thermotherapy: dry heat and moist heat. Dry heat includes dry heating packs, hot water bottles, gel packs, and electric heating pads which may work best for local or small areas of pain. Moist heat includes items such as steamed towels, damp heat packs, or hot baths. In general, moist heat is preferred over dry heat as it heat conducts better and penetrates deeper to reach muscles, ligaments, and joints. It is, however, important to remember that superficial heat therapy does not sufficiently raise the temperature of deeper muscle and other tissues. Warm compresses significantly increase tissue temperature of the lumbar region (>2°C or >35.6°F) at 0.5 cm and 1 cm depths but heating was minimal at 1.5 cm depth [5]. Exercise is the best means to increase blood flow to skeletal muscle [33].

Heat therapy should be avoided during the acute inflammatory phase of healing (within 48 to 72 hours after injury) when inflammation, swelling, or bruising is present, and the skin is warm or hot to touch or in an area of recent bleeding. Heat applied too early potentiate swelling, inflammation, and pain. Thermotherapy is better used during the subacute and chronic phases of the healing process known as the proliferative and remodeling phase, respectively. During these phases, the benefits of using heat therapy include relieving pain, increases blood flow, reducing muscle spasms or tightness, increasing flexibility and range of motion, and enhancing tissue healing.

Before treatment, the therapist should test the temperature of the heat therapy agent by placing the item on back of the therapist’s neck to check to make sure it is not hot or too warm. A thin towel or other material (e.g., shirt or pillowcase) is commonly placed between the heat source and the skin. Slightly moist towel may increase the conductivity of heat. During treatment, the patient should be repeatedly monitored for its comfort level, and the skin observed for excessive response, such as redness, blistering, signs of burning, and red mottled skin. Risk of burn increases with decrease in the amount of subcutaneous fat because fat serves as an insulator. Thermotherapy generally last from 10 minutes to a maximum of 15 minutes each session. The treatment may be repeated three or four times daily or as needed depending on severity of injury, stage of tissue healing, area of the injured tissue, and desired outcome. Thermotherapy agents typically heat the skin and subcutaneous tissues to a depth of 1 to 2 cm. For deeper tissues (>2 cm depth), therapeutic ultrasound with continuous frequency is recommended. The most desired effects of heat are achieved when the temperature is increased between 2 and 4°C in the tissues. Temperature of tissue that is greater than 45°C (113°F) can be painful and cause irreversible damage.

Precautions and contraindications of cryotherapy are as follows:

Precautions for the use of thermotherapy:

  • Very young and very old patients
  • Small animals or extremities
  • Pregnancy
  • Obesity
  • Impaired circulation
  • Poor thermal regulation
  • Cardiac insufficiency
  • Over the superficial main branch of a nerve
  • Over an open wound
  • Poor or impaired sensation
  • Hypertension

Contraindications for the use of cryotherapy:

  • During acute phase of tissue healing with swelling and inflammation
  • Acute bleeding
  • Fever or hyperthermia
  • Heat hypersensitivity or intolerance
  • Over tumor or malignancy
  • Over-regenerating peripheral nerves
  • Over an area with circulatory compromise or peripheral
  • Vascular diseases


Thermal energy modalities are commonly used in animal rehabilitation. They are applied to connective, muscle, and soft tissues to cause either a tissue temperature to decrease or increase in order to achieve a therapeutic effect. Cryotherapy reduces blood flow, decreases nerve conduction velocity, increases pain threshold, inhibit muscle spasticity, and decreases enzymatic activity rate. These effects of cryotherapy are used clinically to control or reduce inflammation, pain, edema, and muscle spasm. Thermotherapy, on the contrary, increases blood flow, increases nerve conduction velocity, reduces muscle guarding, increases extensibility, and increases the enzymatic activity rate. These effects of thermotherapy are used clinically to control pain, relax muscles, increase soft tissue flexibility and stretching, and accelerate healing. Subcutaneous fat acts as a major thermal barrier between the skin and deeper soft tissues, adjustment of treatment duration is required with overweight and obese patients. There remains an ongoing need for more sufficiently powered high-quality randomized control trials on the effects of cold and heat therapy.


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Part II

Ronald B. Koh* and Janice Huntingford

* Corresponding author


Photobiomodulation (PBM), photobiomodulation therapy (PBMT), uses non-ionizing light sources in the visible and infrared spectrum (such as lasers, LEDs, and broadband light), is a rapidly growing treatment modality used for a variety of medical conditions in companion animals. PBMT is painless, noninvasive, and easily administered in a primary care setting to accelerate healing in a number of tissues, provides analgesia, and decreases inflammation through modulation of immune and inflammation responses [1]. PBMT has been used in human and veterinary medicine to improve wound healing, treat snake bites, decrease pain and inflammation resulting from musculoskeletal conditions, improve neurologic function after trauma or injury, treat stomatitis and other oral inflammation conditions, treat intraoperative and postoperative inflammation, and enhance healing of sport-related injuries [2].

Since its development, PBMT has been referred to by many names; terms such as cold laser, low-level laser therapy, phototherapy, and low-level light therapy appear in the literature. According to the American Society for Laser Medicine and Surgery (ASLMS), photobiomodulation (PBM) and PBMT are accurate and specific terms for its effective and important therapeutic application of light. Hence, the term photobiomodulation therapy was added to the Medical Subject Headings (MeSH) database in 2015, and it is defined as “a form of light therapy that utilizes nonionizing forms of light sources, including lasers, light- emitting diodes (LEDs), and broadband light, in the visible and infrared spectrum.”[3]

Mode of Actions of Photobiomodulation

Evidence suggests that PBMT has a wide range of effects at cellular and subcellular levels, including increasing reactive oxygen species (ROS), adenosine triphosphate (ATP), and nitric oxide (NO) [4, 5]. Increased ROS activates the endogenous antioxidant enzyme systems; increased ATP supplies cells with energy for reparation; increased NO promotes angiogenesis, modulates the inflammatory and immune responses, and mediates vasodilation [5]. To produce such effects, the light energy or photons must be absorbed by a target cell, specifically intracellular chromophores within the mitochondria, to promote a cascade of biochemical events that affect tissue function. The primary chromophores are cytochrome c oxidase in mitochondria. Cytochrome c oxidase absorbs light energy or photons in the spectrum of 500 to 1000 nm (the therapeutic window of PBMT), and breaks the bond with NO, which allows bonding with oxygen and production of cytochrome c oxidase at an optimal rate [5, 6]. Cytochrome c oxidase is responsible for the production of ATP. Additional electrons are accepted by oxygen to produce ROS [7].

The overall clinical effects of PBMT can be summarized as follows:

  1. Promote Adenosine Triphosphate Production

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Jul 30, 2023 | Posted by in ANIMAL RADIOLOGY | Comments Off on Common Therapeutic Modalities in Animal Rehabilitation

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