The spine (vertebral column) is comprised of 4 curves ( cervical, Thoracic, Lumbar and Sacral plus Coccyx) opposing each other. These curves are made up from 34 vertebrae {- 7 cervical vertebrae (Neck), 12 Thoracic vertebrae (Upper and mid back), 5 Lumbar Vertebrae (lower back) , 5 fused Sacral vertebrae and 4 fused Coccygeal vertebrae (tail bone)}, 23 intervertebral discs and associated ligaments and muscles are what maintain the shape of the spine.
The vertebra is divided into two parts: Anterior (front part) and Posterior (back part).
Between the anterior and posterior parts located the vertebral foramen (spinal foramen). It’s the opening through which the spinal cord passes.
The posterior part of the spine is comprised of spike like structures the Spinous Processes. These processes serve as the attachment of ligaments and muscles.
On the sides of the vertebrae there are the transverse processes which also give the rise and attachment of ligaments and muscles. These structures play a special role in the Thoracic spine as they are attached to the ribs which form the thoracic cage.
Intervertebral Discs which are situated between vertebrae are a jelly like structures which absorbs shocks and help to preserve the height between vertebrae. This height is necessary for the passage of the nerve roots on each side of the vertebrae. These structures deforms with pressure (load) to ensure a smooth movement between the spinal segments.
The Disc is spherical in shape and is made up of two layers : the outer layer is called Annulus Fibrosus a solid membrane that contains a jelly like material (water based) the Nucleus Pulposus which forms the core of the Disc. This formation helps the disc to bear a huge load and transform it to the lower segments of the spine.
Intervertebral Discs deform with loading. When we flex (bend forward) the disc deforms posteriorly (backwards), in extension (bending backwards) it deforms anteriorly (forward) and when we bend to the right it deforms to the left and when we bend to the left it deforms to the right.
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With day to day activity and with aging these discs undergo a wear and tear and some end up losing their flexibility or their optimal height and thus lose their optimal function. However, disc degeneration also isn’t a one category. It is classified according to the condition of the Annulus Fibrosus and the Nucleus Pulposus.
Weakness or fissuring of the Annulus Fibrosus will allow the Nucleus Pulposus to creep beyond normal limits. A disc might creep Anteriorly (forward), posteriorly (backwards – central) or posterolateral ( backwards and to the side). the disc will creep from a weak point in the wall of annulus. If the disc creeps posterolateral it compromises the nerve root of the compressed side. If it creeps posteriorly it presses the spinal cord or the Thecal Sac (lining of the spinal cord) . If it creeps anteriorly it prsesses the Anterior Longtudinal Ligament which is less significant compared to the first two directions.
It is when the disc presses the spinal cord nerve root (posterior or posterolateral prolapse \ protrusion) or the spinal cord ( central) symptoms such as pain, tingling, numbness and weakness might result. This condition is called Radiculopathy. A common example of radiculopathy is Sciatica which results when the sciatic nerve ( originates from L5-S1 nerve roots) is compressed. Disc problems are commonly seen in the Lumbar spine more in the lower lumbar (L4-L5-S1) region where most of the body weight is transferred to. It’s less commonly seen in the Cervical region and rarely occur in the Thoracic region.
Discs can be classified into 3 main groups:
- Disc protrusions: in this group the annulus fibrosus is intact and the nucleus pulposus is contained but it protrudes through the weakened wall of the annulus .
- Disc prolapse (Extrusion): in this group the annulus fibrosus exhibits radial or circumferential fissuring allowing the nucleus pulposes to escape into the vertebral canal. The exposure of pain sensitive structures in the spinal canal to the leaked nucleus will result in irritation of the affected structure(s).
- Disc Sequestration: it’s a progression to prolapsed disc in which it degenerates and the intervertebral space height is reduced.
Facet joints are small joints situated in the posterior part of the vertebra on each side. They are responsible of directing the movement between vertebrae and thus ensure smooth gliding. As a general rule these joints open with bending forward and close with bending backwards. When the body bends to the right the right facet joint closes while the left facet joint opens and the opposite occurs when bending to the left. The opening and closing of these joints becomes more complex with combined or twisting movements of the back increasing the possibility for these joints to get locked which is known as facet joint impingement.
The ligaments are strong fibrous bands which attach the spinous processes, Transverse processes, and the vertebral bodies thus preventing excessive motion. They play major role along with muscles in the stability of the spinal segments by restraining excessive movement at these segments. For example, the Anterior Longtudinal Ligament (front) which covers the anterior surface of the vertebral bodies is taut in extension (backward bending), the Posterior Longtudinal Ligament (back) and Ligamentum Flavum are taut in flexion.
On its way from the top down, the spinal cord starts to give branches Nerve Roots to the right and left which are responsible for supplying the target muscles and organs. Each nerve root has two branches: Sensory Nerve which is responsible of carrying sensory signals from sensory receptors (located in skin, muscles, joints, ligaments …. etc) to be interpreted by centers in the spinal cord or the brain and Motor Nerve which is responsible of carrying orders to target muscles to induce movement.
Muscles. Back and abdominal muscles originate from the Pelvis insert on different levels on the spine and ribs are responsible for moving the spine and protecting the internal organs.