The dentate ligament cord-distortion phenomenon

The dentate ligaments are small, triangular, 21-paired lateral bands of dural tissues representing extension of the spinal cord pia matter to the dural sheath, and are located midway between the dorsal and ventral attachment of the spinal cord. They functions as anchors that attach the spinal cord to the dura and keep it in a central position. These ligaments are found in the cervical, thoracic, and lumbar regions, and they are thicker in the cervical region than those ligaments seen in the thoracic and lumbar regions

Human mesenchymal tissues, including the dentate ligaments, are affected by Davis’s law which states that: soft tissue will model according to the imposed demand. This means that the ligament will hypertrophy or thickened if it is subjected to chronic stress load. Dysfunction of the dentate ligament can cause neurological dysfunction based on two main theories presented by Grostic (1988):

1. A vertebral malalignment of C2-C3 will exert abnormal traction forces over the dentate ligament at the spinal cord lateral sides. This ligamentous traction will exert forced on both sides of the spinal cord causing “Flattening” of the spinal cord at its anterior-posterior sides (Poisson’s effect). As an effect, the lateral spinal column (tracts) will be irritated (spinothalamic, anterior and posterior spinocelebellar, and may be pyramidal tracts).  The spinocerebellar tract is responsible for muscle tone and joint position, while the spinothalamic tract is responsible for the pain and temperature sensation

In both tracts, the most lateral fibers innervate the most caudal structures (e.g., the most lateral fibers innervate the sacral region, while the most medial fibers innervate the cervical region). Chronic traction forces on the lateral tracts of the spinal cord can result in:

a) Pelvic girdle and lower limb muscles hypertonicity and spasticity due to dorsal spinothalamic tract dysfunction, which in turn manifests as gait abnormality

b) Lower limbs pain and sciatica due to spinothalamic tract dysfunction

c) Amytotrophic lateral sclerosis-like presentation when the traction pressure over the spinal cord is chronic and severe enough to cause lateral spinal tracts degeneration

2. The traction force exerted on the spinal cord veins by the hypertrophic dentate ligament causes collapse of the small radicular veins in the upper cervical cord causing blood stasis and hypoxia in the spinal cord portions drained by these veins. The same pathological mechanism was reported in the literature in the pathogenesis of “Hirayama disease”. Lower levels of hypoxia do not cut off the function of nerves, but increases their susceptibility to neurological dysfunction and hyperexcitability

 

Selected references

1. Eriksen K. Upper Cervical subluxation complex: a review of the chiropractic and medical literature. 2003; Lippincott William & Wilkins; 1 edition

http://www.amazon.com/Upper-Cervical-Subluxation-Complex-Chiropractic/dp/078174198X/ref=sr_1_1?ie=UTF8&qid=1439365311&sr=8-1&keywords=Upper+Cervical+Subluxation+Complex%3A+A+Review+of+the+Chiropractic+and+Medical+Literature

2. Grostic DJ. Dentate ligament-cord distortion hypothesis. Chiropr Res J 1988; 1(1): 47-55

3. Bedford PD et al. Degeneration of the spinal cord associated with cervical spondylosis. Lancet 1952; 2:55-59

4. Khan EA. The role of the dentate ligament in the spinal cord compression and the syndrome of lateral sclerosis. J Neurosurg 1947; 4:191-199

5. Teng P. Myelographic identification of the dentate ligament. Radiology 1960; 74(6): 944-946

6. Tubbs RS et al. The denticulate ligament: anatomy and functional significance. J Neurosurg (Spine2) 2001; 94:271-275