Editor's note: This is a little on the technical side so some readers may get lost with some of the terminology. For some people who are more skeptical and analytical minded this will serve to explain upper cervical care in a more detailed way.
Medullary Lock
by KCUCS.com
The Brain Stem, from a Neuro-Physiological standpoint is the center of life in the body. It is one of the first organized structures formed in embryo (1) and the last place life is evident before a person passes. The lower portion of the Brain Stem lies in the cradle where the head sits on the spine. Therefore, a Head/Neck Misalignment can potentially manifest in a wide variety of symptoms and diseases.
The Medullary Lock is an elaborate network of hard and soft tissue that acts as a stabilizing support for the medulla and upper spinal cord. It secures the medulla and upper spinal cord in the center of the spinal canal and foramen magnum in cases of trauma. Otherwise, even minor slips and falls could be devastating to the body.
With atlas and/or axis misalignment, the very safeguards the medulla and upper spinal cord are afforded through the Medullary Lock become the very mechanism creating cord distortion.
The development of the Medullary Lock was built upon the foundation of Dr. John D Grostic's Dentate Ligament theory (2).
To introduce the Medullary Lock we need to consider 4 basic components.
1. Upper Cervical muscles and their roles
2. Supportive ligaments and membranes and their roles
3. 4 known structures with external attachments to the Dura Mater
4. One structure internally attached to the Dura Mater and intimately connected with the cord.
Each of these components not only work together but are synergistic one with another. There are 4 pairs of muscles called suboccipital muscles (3-5) that act to extend, rotate and laterally bend the Upper Cervical Spine and head. They as well are called proprioceptive muscles because they are chalked full of proprioceptive nerve fibers and carry the responsibility of relaying info to the brain stem as to head position at any given time.
There is an elaborate ligament system that secures the Upper Cervical spine (6-10). The Alar ligament attaches to the lateral margin of the dens about half way up from its base and connects to the medial aspect of the ipsilateral condyle. In the neutral head position these ligaments are in their most relaxed position. The purpose of the Alar ligaments is to check lateral bending and head rotation on the contralateral side. The Alar ligaments do afford some protection for the medulla in checking extreme head rotation. When Alar ligaments are compromised the atlas slides lateral ipsilateral upon lateral bending.
The tectorial membrane works together with the alar ligaments providing stability for the upper cervical region in flexion. The atlanto occipital membrane provides stability in extension. The anterior longitudinal ligament and posterior longitudinal ligament as well provide craniovertebral stability.
The muscles, ligaments, capsules and membranes all provide support for the cranio vertebral region working synergistically. They provide stability and positional awareness for the upper cervical region.
Some of these structures; ligaments, muscles and membranes have direct connection with the dura mater at the cranio vertebral junction. There are four known structures external to the cord that attach to the dura mater.
1. Attachment of the dura mater to the foramen magnum (11)
2. Attachment of the dura mater to the posterior arch of C1 & C2 (11)
3. Connective tissue bridge between the rectus capitus posterior minor muscle and the dura mater (12)
4. Connective tissue attachments between the ligamentum nuchae and flavum to the dura (13,14)
There is one internal structure to the dura mater, the dentate ligament, which stabilizes the medulla and upper spinal cord within the spinal canal space in the upper cervical spine. Dr. Grostic outlined its detrimental effects (2).
The Medullary Lock is a stabilizing factor for the medulla and upper spinal cord (15). The 4 known structures described above external to the dura and the one internal, the dentate ligament, all work together as a network of support. Regardless in what position the head moves, whether rotation right or left, flexion or extension, lateral bending left or right, or any combination, it is important for the medulla and upper spinal cord to remain fixed within their position relative to the spinal canal and foramen magnum. This becomes even more crucial in the cases of trauma. Movement beyond a small amount in the vertical superior or inferior, anterior upon flexion, posterior upon extension or any combination can prove to be fatal. In fact, it is reported that most fatal car crashes are the result of a fractured atlas. In these cases, it is easy to see how the Medullary Lock could lose its integrity.
The Medullary Lock is a mechanism that provides security and stability for the medulla and upper spinal cord. However, because of its mechanism of support, when the upper cervical vertebrae are in a 3 directional torque misalignment, stretch and tension are exerted through the dentate ligaments exerting forces on the cord as described by Dr. Grostic.
Dr. Grostic's dentate ligament cord distortion hypothesis was consistent with what BJ Palmer described (16) in Volume XVIII, regarding cord pressure.
BJ Palmer expounded upon the original 4 elements of a subluxation:
1. Misalignment
2. Occlusion of a foramen
3. Pressure upon nerves
4. Interference to the mental impulse.
BJ explained the necessity of a 5th element (17) describing the subluxation as a 3 directional torque, misaligning on three planes simultaneous. In this manner, the misalignment becomes permanent more or less. It is the permanency of the upper cervical subluxation that leads to the weakened ability of the body to adapt to the environment and grow in dis-ease.
The longer a person is able to stay balanced in the upper cervical area, remaining relatively clear from nerve interference, the stronger the Medullary Lock becomes. The stronger the Medullary Lock becomes the more difficult it is for a person to subluxate and the higher the potential is for that person to recover from long term illness or simply achieve their highest potential health. The reverse is true, the more unstable the Medullary Lock, the more easily it will be for that person to subluxate and the more susceptible the person will be in 'growing dis-ease'.
It is our opinion that over adjusting or adjusting too often, especially with upper cervical procedures, can weaken the Medullary Lock.
KCUCS practitioners view their purpose as Upper Cervical doctors to be guardians of the Medullary Lock, to facilitate more stability of the Medullary Lock over a long period of time. Putting particular emphasis on substantial long-term growth in health and life. This is consistent with what BJ Palmer referred to Accumulative Constructive Survival Value (ACSV) (18). The greater the ACSV, the greater the ability to grow in health, adapt to the environment and overcome disease.
REFERENCES:
1. Sanes DH, Reh TA, Harris WA: Development of the nervous system, 2nd edit. 2006, Elsevier Inc. Burlington, MA ISBN: 978-0-12-618621-5.
2. Grostic JD: Dentate ligament - cord distortion hypothesis. CRJ Vol 1(1): Spring, pp 47-55
3. Gray H, Pick TP, Houdin R: Gray's Anatomy: The unabridged running press edition of the American classic. ISBN: 0-914294-08-3.
4. Hallgren RC, Fernandez C: Suboccipital muscle contribution to tension-type headache chapter 7 in diagnosis and management of tension-type and cervico-genic headache. Jones and Bartlett, Sudbury, Massachusetts, 2008.
5. Hallegren RC, Andary, MT, 2008. Under-shooting of a neutral reference position following cervical motion in the sagittal plane. J Manipulative and Physiol Ther, 31(7):547-552.
6. Bogduk N, Mercer S: Biomechanics of the cervical spine, I: normal kinematics. Clin Biomech (Bristol, Avon). 2000; 15:633-648.
7. Dvorak J, Panjabi M, Gerber M, Wichmann W: CT-functional diagnostics of the rotatory instability of upper cervical spine, 1: an experimental study of cadavers. Spine, 1987; 12:197-205
8. Penning L: Kinematics of cervical spine injury: a functional radiological hypothesis. Eur Spine J. 1995; 4:126-132.
9. Swartz EE, Floyd RT, Cendoma M: Cervical spine functional anatomy and the biomechanics of injury due to compressive loading. J Athl Train. 2005 Jul-Sep; 40(3): 155-161.
10. Singh AP: Biomechanics of upper cervical spine. Bone & Joint. Feb 10, 2010, http://boneandspine.corn/spine/cervical-spine/biomechanics-of-upper-cervical-spine/
11. Hinson R, Zeng ZB: Epidural attachments in the Upper Cervical Spine. Abstracts from the 15th Annual Upper Cervical Spine Conference, November 20-21, 1998, CRJ, 1999;6(1):31-32.
12. Hack G: Anatomical relation between the rectus capitus posterior minor and the dura mater. Spine, 20(23): 2484-2486
13. Shinomiya K, Dawson, J, Spengler DM, Konrad P, Blumenkopf B: An analysis of the posterior epidural ligament role on the cervical spinal cord. Spine, 1996; 21(18):2081-2088
14. Dean N, Mitchell B: Anatomic Relation between the nuchal ligament (ligamentum nuchae) and the spinal dura mater in the craniocervical region. 2002 Clin. Anat. 15:182-185.
15. Kessinger, R: KCUCS instrumentation module notes. 2009, Cape Girardeau, MO, pp 20-23.
16. Palmer BJ: The subluxation specific the adjustment specific, Vol. XVIII. 1934, Palmer School of Chiropractic, Davenport, IA. pp 322-323.
17. Palmer BJ: The subluxation specific the adjustment specific, Vol. XVIII. 1934, Palmer School of Chiropractic, Davenport, IA. pp 248-251
18. Palmer BJ: History repeats, Vol. XXVII. 1951, Palmer School of Chiropractic, Davenport, IA. pp 707-708.
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