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Figure 1: Diagram of an Upper Level Lumbar Vertebra.

The Left image is a cross-sectional (Axial) View. The image on the Right is a "side" or Lateral View.

The Spine is composed of individual bones (Vertebrae) stacked one on top of the other in a column. Each vertebra consists of an oval shaped Vertebral Body, which lies in the front (anterior) part of the vertebra. The Vertebral Body is the major weight bearing portion of the vertebra. The back (posterior) portion to the vertebra consists of an arch of bone (Lamina and Spinous process), which protect the Spinal Cord and its coverings. The bony arch of each vertebra is connected to the body by two small columns of bone (Pedicles). The Spinal Canal (the circular center portion of the vertebra) is formed by the two (2) Lamina (lying on either side, in the back), the Pedicles on both sides and the Vertebral Body in the front. The Spinal Cord and its nerve roots are contained within the Spinal Canal and are covered by a dense, fibrous, tubular membrane called "Dura Mater". The Spinal Cord and its nerve roots are surrounded (within the Spinal Canal) nourished and protected by a clear and colorless fluid, the Cerebrospinal Fluid (CSF).

Figure 2: Cervical Spine Cross-sectional Anatomical Diagram

One convenient way to understand this anatomy is to consider that the Spinal Cord and Spinal Nerves are structures that "live within a house made of bone" (the Spinal Canal). The "roof of the house" is formed by the Lamina. The "walls" are formed by the Pedicles and the "basement" by the Vertebral Body. A pair of Spinal Nerves will exit the Spinal Canal (one on either side) at every vertebral level through "windows" in the "walls" (called "Foramen") which are formed by the Pedicles of adjacent vertebrae.

The vertebrae are separated one from each other by the intervening "Disc" which acts, in part, as a "shock absorber" as well as part of a joint system that permits motion. The disc is made up of two main parts. The "shock absorber" portion is the central "Nucleus Pulposus". Under age twenty, this entity is quite rubbery while over age 50, it becomes more like crab meat as it looses some of its resiliency, elasticity and progressively dehydrates. The Nucleus Pulposus is held in place by a very dense, thick, multi-concentric ring capsule, called the Annulus Fibrosis. It is the Nucleus Pulposus that is involved in conditions of "herniated disc".

Figure 3: Diagram of an Intervertebral Disc.

The centrally located Nucleus Pulposus acts like a "shock absorber". Its "rubbery" consistency ultimately degrades with age and "use" resulting in a process of "dehydration" which then imparts a quality similar to "crab meat".

The Annulus Fibrosis is a thick, multi-layered, tenacious capsule that confines the Nucleus Pulposus. See Figures 4A & 4B below for the changes to these structures in Extruded Disc situations.

In most patients who suffer a "herniated disc" (synonymous terms include "ruptured", "misplaced", "displaced", "bulging", etc.), the central Nucleus Pulposus is pushed backwards towards the Spinal Canal and stretches the Annulus Fibrosis as well as the overlying Posterior Longitudinal Ligament. This is usually quite painful and results in a powerful contraction of the strong (Paravertebral) muscles that run vertically along the length of the spine and are attached to each Lamina. In some cases the contractions are strong enough to cause the patient to involuntarily "bend" to one side (a condition known as "Scoliosis"). If the "bulging" disc strikes the nerve root, it will be even more painful with pain "radiating" along the path that the nerve travels (either into the arm, in the case of a Cervical Herniated Disc or into the buttock and/or leg, in the case of a Herniated Lumbar disc).

"PAIN" and "MUSCLE SPASM" are normal body defense mechanisms. Oftentimes, physicians treat the symptoms without initiating the investigative process to identify the underlying cause. In the event of severe persistent pain or the onset of some neurological symptoms (tingling, numbness or weakness) or the appearance of bowel or bladder symptoms, then Neurological evaluation including Neuroimaging techniques is appropriate.

For the vast majority of patients, these herniations are self limiting and will reposition themselves since the Posterior Longitudinal Ligament and the Annulus Fibrosis are "elastic" and quite strong. This repositioning can be assisted by any of several methods including having the patient lie down to take the entire upper body weight off the ruptured disc thus removing its load bearing requirement. Traction devices can accomplish the same thing and are particularly useful for Cervical Spine problems.

In the event that the herniated disc actually tears a hole in the Annulus Fibrosis and the Posterior Longitudinal Ligament, the condition is called an "Extrusion". This is considerably more serious since the disc cannot reposition itself, a circumstance similar to "toothpaste coming out of its tube." In this case the extrusion can cause considerable injury to the nerve root(s) and/or the Spinal Cord. This becomes a surgical problem.

Figure 4A (Left): Diagram of an Extruded CERVICAL Disc.

In this illustration the disc is extruded to the side (laterally) resulting in severe compression of the Nerve Root but not the Spinal Cord. (Note the difference here regarding the contents of the Spinal Canal compared to Figure 4B where there are ONLY NERVE ROOTS within the Dural sheath.)

Figure 4B (Right): Diagram of an Extruded LUMBAR Disc.

The Nucleus Pulposus escaped the confines of the Annulus Fibrosis (Arrow) and the Posterior Longitudinal Ligament resulting in compression of the nerve root.

Degenerative Arthritis (osteoarthritis) is another among the conditions of the Spine with which one should be familiar. As the disc "wears" either through significant trauma or just the "trauma of daily life", there is a certain amount of "wear and tear", not unlike what one would expect in the shock absorbers of ones vehicle. Over time the disc looses some of its resiliency and hydration. As this happens, it also "shrinks" causing the adjacent vertebra to come closer together. The bones at these joints are then rubbing against each other. Unlike ball bearings of mechanical joints which will become destroyed, our joint bones respond by developing "new" bone. This new bone is called "Bone Spur" which then presses into the Spinal Canal and/or the Spinal Foramina resulting in pressure against the nerves (and/or Spinal Cord). This pressure could become a significant problem requiring surgical attention.

Figure 5: Diagram of Lumbar Vertebrae with their Ligaments.

The "cutaway" portion demonstrates the disc structure with related ligaments as well as the Foramena with their ligaments.

The vertebrae are connected together through several structures including bone joints (the "Facets" which are located on the back portion of the vertebrae on either side), the "Disc" and by several "Ligaments". The ligaments are very strong structures which run the entire length of the Spinal Column from top to bottom and virtually encircle the "Vertebral Body". There is a ligament running the entire length of the Spinal Column in the front (the "Anterior Longitudinal Ligament"), the back (the "Posterior Longitudinal Ligament") as well as along the sides (the "Lateral Longitudinal Ligaments") attaching one vertebra to the next. In the event that a ligament should fail at one or several levels (usually as a result of trauma or consequent to advanced degenerative changes) then the vertebral alignment may fail resulting in a condition of "instability" and "misalignment". Among the degenerative changes that affect the ligaments is the deposition of "Calcium" as part of the metabolic process of "degeneration". This, as well, can make the ligament weaker and/or create pressure upon nerves roots (and/or Spinal Cord).

Figure 6: Anatomical Diagram of the Spinal Ligaments.

Another series of ligaments that connect one vertebra to the next is located just "underneath" (or anterior) to the Lamina. This is the "Ligamentum Flavum" (or "Yellow Ligament"). As part of the degenerative process that affects the Facet Joints over time, this Ligamentum Flavum can also become quite thickened and possibly calcified which may result in undue pressure being placed upon nerve roots and/or Spinal Cord.

Figure 7: Anatomical Diagram of the spine, Spinal Cord and Spinal Nerves.

A pair of Spinal Nerve Roots leaves the Spinal Canal, one on either side, at each vertebral level. The Spinal Cord "ends" in most people between the T12 to L2 levels. In the Cervical and Lumbar regions, these nerve roots combine in a characteristic manner to make up the various nerves that supply the muscles of the arms and legs. In the lower Lumbar region, these Spinal Nerve Roots combine to form the Sciatic Nerve.


Please consult the more comprehensive reviews relating to Cervical and Lumbar Spine Disorders on this website for further information.

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This page last edited on 2/19

All content ©2022 by Neurosurgical Consultants, P.A.
Author, Martin L. Lazar, MD, FACS
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