- The peripheral structure, or site of the injury.
- Presynaptic inhibition within the spinal cord at the segmental level.
- Enkephalin mediated pain control involving brainstem, hypothalamic, and pituitary structures.
Decreased Response from Peripheral Structures
Decreased responses from peripheral structures may be obtained through the use of superficial heat modalities (infrared, hydroculation, fluidotherapy and hydrotherapy, diathermy, and ultrasound). Superficial heat in the management of peripheral pain is advocated because it provides pain relief, reduces muscle spasms, increases blood flow, and helps resolve inflammatory exudates, infiltrates, and edema.1,3 Heat is useful in the reduction of skeletal muscle spasm secondary to underlying joint and skeletal pathology and nerve root irritation.2 Stimulation of the skin with heat produces relaxation by decreasing gama fiber excitability which results in decreased spindle cell activity.2 The decrease in spindle cell activity aids in relaxing muscle spasms and helps to break the pain/spasm/pain cycle. Superficial heating devices which raise the skin temperature also act to reduce muscle spasms.3
Cryotherapy has been shown to produce reflex attenuation of pain response from peripheral structures by having a direct effect on the peripheral unmyelinated and myelinated nerve endings. The application of cooling to the muscle has an effect on the neuromuscular junction by first affecting the smaller, myelinated nerve fibers responsible for spindle cell transmissions. The decrease in temperature is directly related to spindle cell responses, with the decreases in discharge rates from muscle spindles dropping proportionally with the drop in temperature of the structure.2,3 The application of cooling has a general effect on all nerve structures, but has the fastest effect on the spindle cell innervation and the slowest effect on the pain fibers. Therefore, cooling modalities may also be employed to manage skeletal muscle spasms secondary to underlying joint and skeletal pathology secondary to nerve root irritation.
Traction and intersegmental traction modalities produce their attenuating effects on peripheral structures via the pumping action provided by the various units on the market. These systems provide stretch to muscles and separation of joints to help break the pain/spasm/pain cycles by alleviating signals emanating from spasming muscle and irritated joints.4
Similarly, massage has the effect of sedation of pain and relaxation of muscle spasms via the attenuation of trigger points and other foci of irritation within the muscle.2
Presynaptic Inhibition
Presynaptic inhibition is initiated via depolarization of mechanoreceptors within the joint capsules, muscles, musculotendinous interfaces, subcutaneous tissue, and skin. Modalities which stretch, mobilize, or vibrate tissues have the ability to activate these mechanoreceptors which, when activated, have the ability to inhibit incoming pain transmissions from the injury site. This inhibitory action takes place within the dorsal horn of the spinal cord, at the segmental level, and also blocks ascending pain transmissions to higher centers of the central nervous system.5 The electrical modalities and acupuncture create their presynaptic inhibition by activating the faster conducting fibers (which carry mechanoreceptor information) rather than by physically moving the joints and surrounding tissues.
Enkephalin Mediated Pain Control
Enkephalinergic mediated pain control involves activating brainstem structures responsible for enkephalin production. Experimentally, analgesia has been produced by electrical stimulation of the skin, peripheral nerve trunks, dorsal and ventral columns of the spinal cord, thalamus, cortex, periaqueductal gray matter of the midbrain, and the nucleus raphe magnus of the medulla.6 The modalities cited in the chart below produce the necessary stimulus which leads to enkephalin mediated pain control for the patient.6,7 Thus, the doctor can, by using the guidelines presented in the chart, rationally couple modalities to provide optimal coverage of the body's "neurological target sites" for pain control. There are other effects of physiological therapeutic modalities which should also be considered, but they are beyond the scope of this paper.
References
- Kloth, L., and Morrison, M. Therapeutic Microwave and Shortwave Diathermy. United States Department of Public Health and Human Services, Rockville, Maryland, December 1984.
- Wall, P., and Melzack, R. Textbook of Pain.
Churchhill-Livingston, New York, 1984. - Lehmann, J. Therapeutic Heat and Cold, 3rd ed. Williams and Wilkins, Baltimore, 1982.
- McKechnie, B., and Thompson, J. "Therapeutic Effects of Intersegmental Traction: A Radiographic Case Study of Lumbar Joint Motion." Texas Chiropractic Association Journal, November 1989.
- Wyke, Barry. "Neurological of the Cervical Spine Joints." Physiotherapy 1979; 65(3).
- Mountcastle, V. Medical Physiology, 14th ed. C.V. Mosby, St. Louis, 1980.
- Nieuwenhuys, R., et al. The Human Central Nervous System. Springer-Verlag, New York, 1988.
Brad McKechnie, D.C., D.A.C.A.N.
Houston, Texas
Editor's Note:
If you wish to contact Dr. McKechnie writ to: Texas Chiropractic College, 5912 Spencer Hwy., Pasadena TX 77505
Physiological Therapeutic Modalities: Nervous System Target Sites | |||
| Modality | Decreased Response From Peripheral Structures | Presynaptic Inhibition | Enkephalin Mediated Pain Control |
| Superfical Heat | Minimal Increased Threshold of Cutaneous Receptors | Minimal | Minimal |
| Through Spindle Cell Relaxation | |||
| Cryotherapy | Decreases in Motor and Sensory Nerve Conduction Velocity | Yes | Minimal |
| Analgesia Via Decreases in Muscle Afferent Activity | |||
| Axial Traction | Minimal Through Muscle Stretch | Yes | No |
| Massage | Through Attenuation of Muscle Stretch Reflexes by Mechanical Massage and Trigger Point Deactivation | Yes | Minimal |
| Intersegmental Traction | Through Attenuation of Muscle Stretch Reflexes by Mechanical Massage and Trigger Point Deactivation | Yes | Minimal |
| Low Frequency (1-1000 Hz) | |||
| Low Volt | Indirect Through Motor Fatigue | Yes | Yes |
| High Volt | " " | Yes | Yes |
| Medium Frequency | Indirect Through Motor Fatigue | Yes | Yes |
| T.E.N.S. | Minimal | Yes | Yes |
| Acupuncture | Minimal | Yes | Yes |