Using Heat Therapy
Every athlete has faced injury at some time. Soft tissue disorders, such as bruises, tendonitis, bursitis, and fibrositis, can result from overuse, wear and tear, or from a sudden trauma. Sudden trauma results in an acute injury, defined as a situation of short duration. A chronic injury results when clinical signs are allowed to persist or the onset of the injury is drawn out over a period of time. Acute injuries are treated with ice and compression, while chronic injuries are often treated with some form of heat.
Therapeutic ultrasound can be used to increase tissue temperature at depths ranging from three to five centimeters.
Arthritis, perhaps the most common chronic disease, begins as an inflammatory process in the joints and progresses as a degenerative process due to wear and tear and metabolic influences. There is a progressive loss of cartilage followed by a bony reaction. The soft tissue around the joint is weakened as pain inhibits forceful muscle contraction and support.
Tendinitis, bursitis, and arthritis can overlap and all exist at the same time, making diagnosis and treatment difficult. The usual approach in coping with these disorders is to try first one thing, then another to see what will help. Weeks pass and the problem remains.
The horse presents a special challenge to diagnosis and treatment due to his ability to adapt and to compensate. When faced with pain in one area, the horse shifts his weight away from that area. This results in more strain elsewhere and disuse atrophy in the painful area. Eventually the compensatory changes are exhausted and lameness results. The horseman is finally made aware of a discomfort that has been growing over an extended period of time. The injury process is now chronic and involves several structures.
Tendinitis is an inflammatory disorder of the structure that connects muscle to bone. The tendon is not generally as extensible as muscle and is susceptible to strain. The muscle-tendon junction also can be a site of strain. In some cases, tendon sheath inflammation is a more appropriate term for the condition, if the inflammation occurs in the tendon sheath, rather than the tendon itself. Should this condition be allowed to persist, fibrosis can occur in the sheath and extend to the tendon, restricting motion.1
Bursas are fluid-filled pouches that reduce friction over pressure points. Inflammation of the bursa (bursitis) usually results in extra fluid production, heat, and pain. Over time, scarring might occur resulting in pain, restricted motion, and changes of function. Bursitis often is secondary to tendinitis or long-standing arthritis and is a result of overuse strain.
Injury to a sensory nerve results in pain while injury to a motor nerve results in reduced function. Nerves might be injured from stretching or compressing them, or by inflammation surrounding the nerve. This inflammation can reduce blood supply to the nerves, another source of pain. If inflammation of nerves (neuritis) persists, the fibers can atrophy (shrink) or scar tissue might develop, reducing nerve conductivity. Heat, applied during these processes can potentially relieve the sources of the problem and improve nerve function.2
Another troublesome condtion is scar formation within the joint capsule, which might result when the joint function is compromised and movement is reduced. When pain restricts motion, the fascia and connective tissue surrounding the joint shorten. Joint range of motion is reduced by the tight joint capsule, setting the stage for further muscle atrophy.
As you can see, the degenerative cycle of chronic injury is not easy to break. The most efficient approach is to deal with the process in the earliest stage possible. This means daily assessment of the horse's health status and early diagnosis by a veterinarian when a problem is suspected.
Successful treatment begins with an accurate diagnosis. Diagnostic tools such as thermography, ultrasound, and scintigraphy can identify the inflamed structures with accuracy that was not previously possible. Chances of successful treatment are greater if an injury is addressed in the acute phase, which can be as short as two days. During this time, ice, rest, support, and proper veterinary treatment can control early symptoms. Once the condition becomes chronic, one is often faced with addressing a combination of disorders, none of which will subside until they are all addressed.
In the chronic stage of injury, it is essential to address the cause of pain and dysfunction, not just the symptoms. An effective modality that has multiple benefits is heat. All of the disorders mentioned above have the common denominator of pain. Pain is due to muscle spasm, reduced circulation, and nerve pressure caused by connective tissue changes. Heat can address all of these causes and stimulate the repair process. Heating the tissues prepares them for mobilization exercises, facilitating a greater range of motion through reflex pain relief and connective tissue softening.
Heat can be used to neutralize trigger points, a nodule of tender muscle and a source of muscle pain. Treatment of trigger points is aimed at increasing local circulation so the irritated muscle spindle at the heart of the trigger point has sufficient energy to relax. Warming the musculature causes a reflex relaxation of the muscle fibers.This can be further augmented by stretching to relieve the tight band of muscle in which the trigger point is located.
Therapeutic heat is a universal treatment in chronic injury, yet sources of therapeutic heat often are difficult to come by in a barn or racetrack situation. Because of the effects on circulation, metabolism, and nerves, heat plays a vital role in rehabilitation of chronic injuries. It is safe to apply heat when there has been no increase in swelling for 24 hours.
Effects Of Heat
Heat, being a form of energy, increases metabolic activity in the cells. This increased activity causes an increase in oxygen demand locally. As a result, capillary dilation occurs to increase the amount of blood that brings oxygen and nutrients to the area. Membrane diffusion and enzymatic activity also increase, enabling oxygen consumption and waste removal. The waste products of injury include prostaglandins, bradykinin, and histamine, all implicated in nerve fiber sensitization and pain.
Arthritic joints respond favorably to applications of external heat. Joint stiffness is reduced due to a decrease in synovial fluid viscosity and an increase in the distensability of the surrounding connective tissue. The increased temperature of the sensory nerves in the skin overlying the joint will create a reflex pain-inhibiting effect as rapidly sent messages of heat are recognized in the brain, blocking out pain messages. The threshold of sensory nerve endings is elevated, resulting in long-term pain relief.3
Prior heating will facilitate comfortable exercise when connective tissue contractures or scar tissue exists around a joint, limiting its movement. Heating dense connective tissue affects bonds between collagen molecules, making the tissue more pliant. This allows more even distribution of force throughout the entire tissue, reducing focal points of stress, rupture, and inflammation.4 Joint extensibility will increase when heating and stretching are carried out repeatedly over a period of time.
How does one know how much heat is enough? In order to achieve a significant change in metabolic rate and collagen distensibility, temperature of the target tissue must rise at least 5 Fahrenheit. Temperature increases greater than 12 F create the sensation of pain rather than of heat. Unfortunately, by the time pain is registered and the horse attempts to move away, some damage might already have been done. A horse's skin temperature is generally 90-92 F. The heat source must be warmer than this, obviously, to increase tissue temperature. However, it is well documented in human therapy that heat applications of more than 133 F for prolonged periods will cause skin damage. For humans, there is a nine degree "window," or therapeutic range, between effective heating and surface tissue damage. Using this as a guide will prevent over-heating the superficial tissues of the horse.
Methods of heat application include heating pads, hot water bottles, hydrocollator packs, instant chemical heat packs, heating lamps, hot water whirlpools, hot towels, counter-irritating liniments, and therapeutic ultrasound. Of all the heating devices listed, only ultrasound has the ability to penetrate through the skin to the deeper structures such as joint structures, bursa, tendons, and muscles. All the other sources of heat only penetrate the skin and perhaps the underlying connective tissue, structures not involved in most sports injuries.
When using any heating modality, it is important to understand the depth of penetration of the heat produced. Temperature in the injured tissue must increase to have a significant effect on the condition. There is little change in skeletal muscle blood flow with superficial heating agents.5 Because of this, superficial heating agents should be combined with exercise to provide a deep heating effect.6
To illustrate this point, I'll draw an example from a lecture given by Britain's renowned equine therapist Mary Bromiley.7 When a horse or human has back pain of muscular origin, it is the multifundi muscles that likely are irritated. These muscles are a series of small bundles of muscle fiber that extend from the transverse processes of a vertebra to its neighbor's vertebral spines. They lie under the larger structure of the longissimus dorsi muscle. Fascia and the skin lie over this. Heat from most of the therapeutic sources will be absorbed mostly in the skin and fascia, with little heat getting past the longissimus dorsi muscle. The multifundi muscles might not receive any direct therapeutic benefit from the more superficial forms of heat. In this case, exercise directed at the multifundi can affect the comfort level and strength of the back and a heating modality can facilitate the exercise.
Use Of Superficial Heating Devices
The pros and cons of the available products should be considered when equipping your barn with some form of heating device. Electric heating pads, although comforting for people, might not be a good choice for use on a horse. Because they must be plugged into a wall outlet, there is the danger of the horse stepping on the cord. Metal horse shoes have been known to cut through electric cords and cause fatal shock.
Another problem is that the handler does not know exactly how much heat is being delivered and absorbed. Skin burning could occur unless one is in constant attendance during the 20-30 minute recommended treatment time and continuously checks under the pad to monitor the heat build-up. Once the skin is burned, you have two injuries to contend with instead of one.
Hot water bottles can present problems as well. They are not of the size and shape to be used with ease on a horse. When wrapped on the limbs or tucked under a blanket, they have a tendency to slip down or fall out. Should the stopper accidentally come out, you have the danger of scalding.
Single leg whirlpools are designed specifically for the horse. Whirlpools provide the effects of gentle massage and superficial heat. The agitation of the water can loosen scar tissue on the skin surface and help remove debris from a wound. An iodine concentrate added to the water will reduce the possibility of transmitting infections and aid in cleansing abraded skin. Of course, the horse should be as clean as possible and the whirlpool boot should be disinfected before use if an open wound is present. A thermometer to check water temperature is essential for safety and effectiveness of hydrotherapy. The water temperature should be between 103-110 F. If a tank is used, it must be plastic or rubber, never metal, to avoid shock hazard. The motor should be grounded and protected with a ground fault interrupter at the wall plug. The danger of shock from ungrounded metal whirlpools is great.8
Hydrocollator packs provide an efficient means of superficial heating. These cotton packs contain a gel that absorbs heated water and become soft in order to conform to the contours of the body. Although they are heavy enough to stay in place under a blanket when treating the horse's back, they are a bit heavy and bulky for the horse's leg. Hydrocollator packs become quite hot as the heating unit can bring water to 150 F. The packs must be wrapped in towels before they are applied to avoid burning the skin. They will hold their heat for about 20 minutes, which makes them much more efficient than hot towels that quickly lose their heat.
Instant chemical heat packs are available. These might be the most efficient means of providing extended applications of heat for use on horses. A plastic pouch contains chemicals that produce heat when they are mixed. No additional equipment is needed and the heat lasts for about 90 minutes. This self-contained heat source becomes quite hot at first, so one should quickly put it in the accompanying cloth sleeve. Sleeves are available to fit various areas of the horse. By soaking the sleeve before inserting the heat pack, moist heat is provided.
Heating lamps can create a fire hazard should they fall into the straw bedding. In the usual situation, hung from a barn rafter over the horse, they do not provide enough penetrating heat to be of much therapeutic benefit. Equine solariums have been built so several lamps fixed to a metal arc can be lowered closer to the horse's back. Horses seem to enjoy standing under them, particularly when the weather is cold and they are sore.
Liniments and analgesic balms are counter irritating agents. These lotions, creams, or liquids contain cutaneous nerve irritating chemicals, usually Caspian from the pepper plant. The irritant causes skin capillaries to dilate, creating the feeling of warmth on the skin surface. This, of course, does nothing for the deeper structures. The massaging required to rub the analgesic balm into the skin could be beneficial and the sensory nerve stimulation could block out some pain message recognition. It must be realized that these agents do not really warm the structures of the joint such as the capsule, where restrictions occur, and their use is not a substitute for pre-exercise warm-up.
It has been shown that dry heat can raise surface temperatures to a greater degree, but moist heat can penetrate to a slightly deeper level of tissue.9 A heat pack can be put over a damp towel if moist heat is desired. For muscle soreness, try adding two cups of Epsom salts to a bucket of warm water. Soak towels in the water, wring them out so there is no dripping, and place them on the sore area. With the addition of a heat lamp or chemical heat pack, the towels will maintain their warmth longer. The magnesium in Epsom salts is an excellent muscle relaxant and sedative for the nervous system. Some magnesium will be absorbed through the skin during a hot towel soak and have a relaxing effect on the muscles.
Ultrasound For Deep Heating
Therapeutic ultrasound can be used to increase tissue temperature at depths ranging from three to five centimeters without over-heating the skin and superficial tissue.10 The effects of therapeutic ultrasound are the same as superficial heating modalities with the addition of a "micromassaging" oscillation of molecules. Sound waves create rapid oscillations that disrupt collagenous fibers and increase cell metabolism. Ultrasound combined with stretching exercises can elongate contracted fascia and reduce the restrictive effects of scar tissue. This effective modality will be described in more detail in a later column.
Effects of Heat
Increases cellular metabolism.
Increases muscle spindle activity.
Increases muscle contractility.
Increases inflammatory response.
Increases extensibility of collagen.
Increases nerve conduction velocity.
Reduces synovial fluid viscosity.
The therapeutic results of these effects are a reduction in pain and muscle spasm, an increase in circulation, more mobile connective tissue, and a general feeling of relaxation and well-being.11
When attempting to use superficial heating modalities on a horse, attention to task is necessary to avoid over-heating the skin and to provide sufficient deep heat to accomplish the treatment goals. Heat applied too soon after injury will increase the inflammation, swelling, and pain. Heat is contraindicated in acutely inflamed joints or soft tissue, but can be safely applied when there is no increase in the swelling over a 24-hour period.
1. Currie, D. M. Self-Directed Learning and Medical Education: A Comparison. Arch Phys Med Rehab. 1985:66, p. 454.
2. Robinson, A. J., and Snyder-Mackler, L. Clinical Electrophysiology. Williams & Wilkins:1995. p. 389.
3. Michlovitz, S. L. Thermal Agents in Rehabilitation. F. A. Davis:1986. p. 270.
4. Currier, D. P., and Nelson, R. M. Dynamics of Human Biologic Tissues. F. A. Davis:1992. p. 68.
5. Michlovitz, p.102.
6. Greenberg, R. S. The Effects of Hot Packs and Exercise on Local Blood Flow. Phys Ther. 1972:52. p. 273.
7. Bromiley, M. Facts About Backs. 12th Annual Bluegrass Laminitis Symposium. Kentucky. 1998.
8. Porter, M. J., and Porter, J. Electrical Safety in the Training Room. Athletic Training. 16:1981. pp. 263-264.
9. Abramson, D. I., et al. Comparison of Wet and Dry Heat in Raising Temperature of Tissues. Arch Phys Med Rehabil. 1967:48. p. 654.
10. Michlovitz, S. L. Thermal Agents in Rehabilitation. F. A. Davis:1986. p. 99.
11. Kaplan, P. and Tanner, E. D. Musculoskeletal Pain and Disability. CT: Appleton & Lang. 1989. p. 83.
About the Author
Mimi Porter lives in Lexington, Ky., where she has practiced equine therapy since 1982. Prior to that, she spent 10 years as an athletic trainer at the University of Kentucky. Porter authored The New Equine Sports Therapy, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
POLL: University Equine Hospitals