Structural Anatomy

The spinal column has classically been divided into several structurally and functionally distinct sections, the cervical spine, the thoracic spine, the lumbar spine and the sacral spine. Largely, this book deals with the cervical, thoracic, and lumbar sections since the sacral section is functionally fused and offers little opportunity for mechanical manipulation except where it interfaces with the lumbar spine at L-5, which is probably the most problematic area in the spine because it is the first mobile segment above the rigid pelvis. (See Figure 5)

It is important here to note the curvature of the spine. It is not a straight linear structure when viewed from the side (or the "lateral" view). The major curves are seen at the cervical and lumbar regions where the majority of flexibility is also present.

One can look upon the spinal column as an incredibly strong central support structure upon which the trunk and upper body rest similar to a long series of bony spools separated by cushions. The spools being named the vertebral bodies and the cushions are the intervertebral discs (or simply referred to as the "disc"). A functional disc unit is comprised of the vertebral bone above and below an interposed disc (see Fig. 6).

The anterior portion of the vertebral column (spools with cushions between them) is a weight bearing, shock absorbing, flexible structure capable of amazing feats of strength. The posterior portion is composed of bony bridges and spikes that protect the spinal cord and nerves, acts both as a moment arm and as a fulcrum, and guides the movement of the functional unit while maintaining the vertebral bones' positions relative to the each other. As can be seen in Figure 7, the anterior and posterior components join at the pars interarticularis to create a canal through which the spinal cord travels and sends its major branches, the spinal nerves, out through spaces called intervertebral foramens. The superior aspect of the intervertebral foramen is composed of one pars interarticularis and the inferior border is composed of the vertebral bone adjacent and inferior to it.

A view looking down on a cross-section of the vertebral bones can be seen in Figure 8 so the reader can understand the relationships between these structures. Especially important is the close proximity of the discs to the spinal nerves. If a disc ruptures posteriorly, it can be easily seen to be capable of impinging upon a spinal nerve root and damaging it, resulting in paralysis and anesthesia.

For the purposes of this book, the posterior elements can be largely ignored. Not that they do not serve as sources of pain such as arthritis (because they contain joints) or sprains (because they have ligaments holding them together); but, in the largest part, the mechanical pain experienced in the spine originates from a degeneration of the stress-dissipating and pressure containment structures known as the intervertebral discs.

Of course, the intervertebral disc (usually referred to simply as the "disc") is not the only structure that dissipates stresses placed on the spine. With flexion, extension, rotation, or shear stress, the load distribution on the entire functional unit is shared by the intervertebral disc, anterior and posterior longitudinal ligaments, the facet joints and the capsule, and other ligamentous structures like the ligamentum flavum and the interspinous and supra spinous ligaments, which attach to the posterior elements of the functional unit. Those anatomical structures other than those directly contiguous with the disc are largely unamenable to mechanical manipulation and don't usually get into trouble without major trauma (by major trauma, I refer to falls off of roofs or major motor vehicle accidents as opposed to minor trauma like lifting garbage cans); therefore, they are outside of the scope of this book. They need not be focused upon in this book because to do so would just be confusing and distract the reader from the major goal of understanding that the most common source of a "bad back" is damage to the disc itself. However, that is not to say that the other problematic entities are insignificant or incapable of producing misery, it is just that the other causes of back pain are both individually and cumulatively in the distinct minority. In fact, if one doesn't achieve relief from practicing the principles of The O'Connor Technique (tm), it is unlikely that a disc is the source of the pain; and I would encourage that category of patient to seek help elsewhere armed with the reassurance that they have probably eliminated disc disease as the origin of their pain.

The spool-like vertebral bodies are held together with tough ligaments that connect bone to bone. On the front (anterior) surfaces lie the anterior longitudinal ligaments and at the back (posterior) surfaces lie the posterior longitudinal ligaments. These two major ligament systems which traverse the spine lengthwise blend at the disc spaces between vertebral bodies with other laterally situated, ligamentous structures of the spine (the lateral intervertebral ligaments) that also run longitudinally along the axis of the spinal column. All these ligaments merge together to circumferentially enclose the more cartilage-like central regions of the disc, forming what is often referred to as a "capsule" at the disc level. This capsule consists of dense, strong fibers that are firmly bound to each adjacent vertebral body. These sheets of ligamentous material blend with the peripheral, most dense, portion of the annulus fibrosus and function to contain both the more gelatinous inner sections of the annulus fibrosus and, in turn, the more liquid nucleus pulposus (See Figures 8 & 9).

This ligamentous capsule, in combination with the concave shapes of the vertebral bones' surfaces, keeps the more internal components of disc material positioned in line with and centrally between the vertebral bodies of the spine. When the body bends forward (flexes), the postero-lateral ligamentous lamina (layers) and the posterior longitudinal ligaments straighten, tighten, and assume a more linear axis, preventing the posterior aspects of the vertebrae from totally separating or coming apart while retaining flexibility. The anterior ligaments perform likewise for the anterior when one bends posteriorly (extends).

Other ligaments which are attached to the processes of the vertebral bodies also function to hold the entire apparatus together; however, they are not as pertinent to the principles of this book because the posterior longitudinal and the intervertebral capsules' ligamentous structures are the fibers which house and keep the cartilaginous disc material from moving posteriorly. Were it not for these ligaments, the discs would have no structural elements to maintain the central disc material positioned correctly between the vertebral bodies. Figure 9 shows these ligaments with their normal structure on the right and their damaged structure on the left. When these structures are damaged, they no longer prevent the central disc material from moving posteriorly, the profound significance of which will become apparent later.

The ligamentous tissues that form the disc's capsule are well-supplied by nerves-- both stretch and pain receptors. This nerve supply enables the brain to know where in space (relative to the other bones) a given bone is positioned, enabling a human to stand erect and balance the portion of the body above the hips with his spine. In contrast to the outer, peripheral, ligamentous structures, the material deep to the capsule, the annulus fibrosus and the nucleus pulposus, do not have a nerve supply (See Figure 10). So, disc pain, when it is present, comes from structures other than the more liquid "cushions" or any other structures deeper than a few millimeters from the surface of the disc. This fact leads some to conclude the common misconception that a patient cannot have pain from their discs. On the contrary, when the disc material that should remain secure within the center presses upon or distorts the ligaments that surround the disc, the pain can be exceptionally intense.

More on pain later; but, for now, it is helpful to understand that the numbered spinal nerves exit the spinal column at the level of the disc inferior to the same numbered vertebral bone. So, the Second Lumbar (L2) nerve and its root (See Figure 7) passes out of the spinal column at the level of the disc below the Second Lumbar Vertebrae through the intervertebral foramen partly formed by the inferior component of its pars interarticularis (also known as a pedicle). The intervertebral foramens are round spaces (between one pars interarticularis and the next) created by the spinal bones through which pass the spinal nerve roots (See Figures 6&8). The spinal nerves supply motor and sensory functions to their corresponding segments of the body. The proximity of these structures to the intervertebral disc is important because if the central disc material herniates and protrudes it can irritate or trap the spinal nerves resulting in pain, loss of sensation, and/or paralysis wherever the effected nerve roots supply innervation. The pattern of this pain is classically described in terms of what structures are supplied by the nerves: dermatomes (areas of skin), myotomes (muscles), sclerotomes (bones, joints, & ligaments) to which the individual nerves for each major spinal nerve travel.

It is technically interesting to know what each spinal nerve innervates so that when pain is felt or function lost it can be localized to a particular spinal nerve and, hence, a doctor can determine which disc protrusion is compressing its corresponding nerve. Such detail is too complex for the intended readers of this book. The reader is free to research any of a number of medical textbooks for this additional information; however I have found this level of expertise confusing and unnecessary to understand the concepts of The O'Connor Technique (tm).

What is important to understand is that each numbered spinal nerve sends a branch (the recurrent sinuvertebral nerve) to the ligaments that surround and contain the disc immediately inferior to the same numbered vertebral bone. The pain and sensory fibers of the discs travel in these nerve branches (See Figure 10). The recurrent sinuvertebral nerve is significant because if pain comes from a disc's ligamentous capsule it travels in that nerve. Pain impulses from this nerve can be interpreted by the brain as coming from the larger, numbered, spinal nerve in which it travels as one of many other different nerves. The implications of this anatomical design peculiarity will become more apparent later, but suffice it to say, here, that this phenomenon can explain why pain in the disc can masquerade as pain in the extremities and why muscles distant from the actual site of disc pain can go into spasm even though the muscle itself has not been actually traumatized. More on this subject when pain is discussed.

It is very pertinent to the understanding of The O'ConnorTechnique (tm) to have a view of the disc in the mind's eye. The intervertebral discs' spherical centers are composed of a gelatinous liquid cartilage material identified as the nucleus pulposus surrounded by an intermeshing laminated concentric fibrous structure known as the annulus fibrosus. The annulus fibrosus is designed with fibrocartilaginous and fibrous protein tissue arranged in concentric layers, each of which attach one vertebrae to the other (See Figure 11). As one moves, anatomically speaking, from the nucleus pulposus to the periphery, the tissues become more dense, stronger, less elastic, less fluid, and more ligamentous until reaching the outermost layers. There, the tissues actually become a tough, capsular ligament.

The laminations of the annulus fibrosus are arranged in bands of tough elastic tissue whose fibers run at oblique angles to the adjacent layers to form a shock absorber (See Figure 12), built like a gelatinous/liquid surrounded by layers of Chinese finger traps. As vertically (axial) directed forces are placed upon a disc's liquid center (nucleus pulposus) it deforms by flattening along a horizontal plane. In this way, the pressure is absorbed and contained by the laminations of the annulus fibrosus. The fibers of the annulus fibrosus are firmly secured to the vertebral bones and mingle with the lateral ligamentous structures as well as the anterior and posterior longitudinal ligaments.

To experience an accurate representation of this structure's consistency, the reader can go to a meat market that stocks large ox tails. Feeling with a finger the center portion of the largest ones and, often in older animal's discs, you can appreciate the liquid character and the central hardened material by pressing the center of the circular white solidified segment. A nearly identical structural design is located in the human disc. By manipulating the hard center structure, one can appreciate how it can be moved with alterations in pressure supplied by the finger. When one bends the spine, forces are placed upon the disc that cause the part-liquid/part-solid, disc material to be equivalently moved.

Further Reading:

Spinal Anatomy
Directional Terminology
Structural Anatomy
Functional Anatomy
Pathological Anatomy
Disc Hydraulics / Mechanics
Compression Forces
Correlation of Mechanical Anatomy with Disc Pain
Traction Forces

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