25 Jan Anatomicophysiological Aspects of Injuries to the Intervertebral Disc

The following is a synopsis of a Research Review by Dan Murphy, D.C. which was published in The American Chiropractor, Volume 33, Number 1, January 2011 The article below was reviewed J Bone Joint Surg Am. 1947 Apr;29(2):461-75.

Destroy the disc and you destroy spinal mechanics.  Therefore, in disc derangement, we are dealing with a dual problem: A.) Deranged spinal mechanics B.) The effects of spinal nerve-root irritation and compression. Nerve root compression results in reduced nerve function, muscle atrophy, and reduced sensation.  Nerve root irritation results in increased pain, increased muscle tone and spasm. The normal nucleus pulposus is 80% water and thus is “incompressible”.  The normal semifluid nucleus transmits forces to the elastic ligamentous structures.  “The critical feature in the disturbance of spinal mechanics and in the production of pain is in the effect on the ligamentous structures, caused by the loss of water or nuclear substance following injury or degeneration(degenerative disc disease). An individual is taller when getting up in the morning due to imbibition(a process whereby the disc takes on water at night to rehydrate).  Men by ¾” and women by ½”.  Due to gravity and being upright and active all day, the nucleus looses fluid throughout the day.  This fluid exchange helps the nucleus and the annulus of the disc to stay healthy. All fluid exchange occurs through the cartilaginous end plate of the vertebral body.  With age, the end-plate becomes less permeable to fluid, the free exchange of water and blood is suppressed, resulting in “progressive desiccation of the nucleus”.  The resiliency of the spine and the motions permitted to it are primarily due to the elastic nature of the annulus fibrosis.  Loss of fluid pressure in the nucleus pulposus leads to grave derangements in the physiology of the disc. The decrease in vertical height of the intervertebral disc spaces leads to subluxation of the interarticular zygopophyseal joints, in which degenerative changes develop as a result of the abnormal forces acting upon them.  The ligamentous structures of the body are very susceptible to pain.  Ligament pain ebbs and wanes and can be accompanied by “vasovagal responses such as nausea, sweating, and fall in blood pressure”.   Deep ligament pain arises embryologically from the mesoderm and causes “sclerotogenous pain”, meaning it does not follow a dermatomal distribution( as compared to sciatica)  Deep slcerotogenous pain can occur in the absence or direct irritation of the peripheral nerve or nerve root.  The annulus fibrosis has been shown to possess rich nerve supply, meaning it can cause pain as well.  Distortion of the annulus(disc bulge vs. protrusion) and other ligaments can cause not only local pain, but also sclerotogenous pain that radiates down the posterior thigh.  This is not “sciatica” because there is no irritation to the nerve roots. Deeper structures of the spine cause slow pain, dull and achy, poorly localized. Nerve compression affects large nerve fibers associated with proprioception and motor function. Pain fibbers are smaller and more likely to fire in response to chemical(inflammatory) stimulus rather than mechanical pressure. Disc herniation without  nerve compression is characterized first by pain, and then a deep ache radiating into the leg in a sclerotomal pattern. Disc herniation with nerve compression is characterized by loss of vibration sense, muscle weakness(if compression is deep enough), reduced tendon reflexes, and hyperesthesia/pain in a dermatomal pattern.  The pain is sharper from chemical irritation of the nerve root affected by the disc herniation. This all indicates that patients can be placed into three categories: A.  Mechanical spinal derangement:  These patients have deep spinal irritations, but no nerve compression.  Typically any referred pain is less intense, does not extend below the knee.  These patients are suffering from a muscle and joint pain syndrome caused by joint dysfunction, joint compression, subluxation, and muscle hypertonicity. B.  Nerve root compression from disc herniation:  Pressure will interrupt nerve conductivity in a precise sequential fashion.  Larger fibers conveying proprioception and motor impulses may be affected first.  Smaller fibers conveying pain, pressure and touch may be affected second. C.  Nerve root compression from spinal cord tumor:  requires surgical decompression and removal. A side note: The McKenzie Method of Mechanical Diagnosis and Therapy classifies three types of pathology: Derangement:  usually involving disc herniation and radicular pain from nerve root irritation and/or compression. Dysfunction: usually involving joint dysfunction, joint compression, muscle hypertonicity, faulty movement. Posture Syndrome:  Poor posture places undue mechanical stresses on otherwise healthy structures. To learn more about McKenzie method: The following two articles by Christie Downing were posted on http://www.mikereinold.com/  These two articles provide a great overview of McKenzie method commonly used in physical medicine and rehabilitation. Part I- Clearing Misconceptions About MDT Part II-Syndrome Classification and Treatment