On The Origin of Atraumatic Neuromusculoskeletal Pain
Written by Editor   
Saturday, November 12, 2016 12:00 AM

The purpose of this study was to examine the possible origins of non-specific or atraumatic back pain by applying the Gate Theory of pain and current physiologic concepts. This study presents a theory that accounts for the initiation and potential consequences of neuromusculoskeletal pain incorporating failure of the mechanism of muscle relaxation and resulting in pain and compromise of the lymphatic system. The theory provides an alternative to current theories and hypotheses of the cause and consequences of neuromusculoskeletal pain.

The incidence of low back and other neuromusculoskeletal pain continues to increase, with low back pain being the leading cause of disability in the world.  In addition to the loss of quality of life for those experiencing musculoskeletal pain, the cost to both patients and society is significant and increasing:

  • The annual cost of chronic pain in the United States, including healthcare expenses (direct medical costs), lost income, and lost productivity, is estimated to be $635 billion. This is significantly higher than the estimated annual costs in 2010, dollars of heart disease ($309 billion), cancer ($243 billion), and diabetes ($188 billion).

  • Total estimated medical costs associated with back and neck pain, two of the commonest presentations of patients with chronic pain, increased by 65% between 1997 and 2005, to about $86 billion a year. Overall, pharmaceutical expenditures related to back and neck pain increased by 188% between 1997 and 2005, but costs associated with prescription narcotics rose by an astounding 423%.

  • In the US, the estimated annual direct medical cost of low back pain is $30 billion. In addition, the impact of back pain is $100-200 billion in decreased wages and lost productivity.

  • Patients with chronic pain have more hospital admissions, longer hospital stays, and unnecessary trips to the emergency department.

Musculoskeletal pain resulting from trauma is relatively easy to understand; however, the cause and, therefore, best treatment for acute or chronic nonspecific musculoskeletal complaints i.e., those complaints that have no known underlying pathology, is elusive. For example, it has been estimated that 90% of low back pain is classified as non-specific. Recasting neuromusculoskeletal dysfunction in light of current pain theory has resulted in the identification of a possible underlying cause or initiating event of non-specific or atraumatic musculoskeletal pain.

It is key to recognize that the perception of pain is not always due to an increase in nociception. Reduced proprioceptive input to the CNS will also result in pain by creating an apparent increase in nociceptive input and this was recently demonstrated experimentally through selective disabling of specific interneurons. A mechanism of muscle dysfunction that results in a reduction of proprioception thereby altering the balance between nociception and proprioception, would provide an explanation of atraumatic pain.

In normal muscle, contraction of individual muscle fibers is initiated through the action of large myelinated nerve fibers which innervate several to hundreds of fibers. Each nerve branch terminates close to the middle of the individual muscle fiber with multiple branches which form the motor end plate. Excitation of these nerve fibers results in the release of acetylcholine which, in turn, open acetylcholine gated channels in the muscle membrane. 

The opening of these channels allows sodium and calcium ions to rapidly pass to the inside of the muscle membrane and depolarize the membrane, resulting in muscle contraction through the generation of an action potential which travels in both directions from the center of the muscle fiber toward each end. Depolarization of the surface membrane of the muscle fiber is accompanied by the release of calcium ions which cause contraction of the myofibrils resulting in contraction of the muscle fiber itself. 

Relaxation of the muscle fiber is enabled by the adenosine triphosphate (ATP) energized calcium pump, which returns calcium ions to the sarcoplasmic reticulum where they are available for the initiation of the next muscle contraction. If the calcium pump malfunctions, the muscle cannot relax. A failure of the calcium pump would account for the inability of a muscle fiber to relax, reducing proprioceptive input to the CNS from the sensory organs of the muscle fiber or fibers involved independently of motor nerve input.

The theory of neuromusculoskeletal dysfunction presented here is comprised of:

  • An acute stage consisting of an initiating event wherein a portion of muscle mass in a normal contractile state is prevented from extending or relaxing due to a local failure of the calcium pump. The inability of the muscle to relax results in the reduction of proprioceptive input to the CNS and the perception of pain.

  • If the muscle dysfunction is not immediately corrected, the initial muscle dysfunction will result in compromise of the lymphatic system resulting in potentially serious and poorly understood consequences for the health of the individual. 

The theory proposed here combines known processes and functions to create a basic building block that may arguably be combined with other components of skeletal function to represent the allopathic trigger point, the osteopathic lesion, the chiropractic subluxation the physical therapy movement restriction and the cardiologist’s myocardial infarction.

A major consequence of the theory presented here is that muscular dysfunction results in a compromise of the lymphatic system. Once the muscle or portion of muscle becomes unable to relax, the lack of movement within the structure of the muscle reduces the drainage of lymph from the cells of the muscle. If the lymphatic system is severely compromised, the cellular metabolism of the affected muscle volume will be altered. Maintenance of the health of the lymphatic system through prevention of compromise of that system by muscle constriction may be the most powerful argument for regular visits to providers skilled in manual therapy.

Failure of the muscle to relax should result in a reduction of the blood flow through that portion of the muscle. The resulting ischemia is likely to result in the generation of recently discovered and as yet poorly understood inflammatory agents which trigger the innate immune system producing increased nociception and therefore increased pain. Since this immune reaction is not associated with invasion of the body by pathogens, this type of inflammatory response is referred to as “sterile” inflammatory response and is associated with mechanical trauma, ischemia, stress and environmental factors. The sterile inflammatory response would appear to be a secondary result of the initial failure of muscle relaxation. Therefore, an expected result of manual therapy that succeeds in reversing the initial muscle dysfunction. 

By starting with the Gate Theory of Pain and applying current knowledge of basic physiology to the problem of back pain, we have arrived at a potentially useful new hypothesis regarding the likely cause of atraumatic back pain. Rather than concluding that all back pain is the result of tissue injury caused by overuse, buckling, trauma, or an aberrant neurological feedback that maintains muscles in a continuous state of contraction, a failure of the mechanism that permits muscle relaxation to occur is proposed. Not being able to exit the contracted state, the normal proprioceptive feedback associated with the involved muscle will be absent resulting in an excess of nociceptive input resulting in the perception of pain. Compromise of the lymphatic system due to lack of normal muscle function may follow. 

Source: http://www.chiro.org/LINKS/ABSTRACTS/On_The_Origin.shtml