Clinical / Spinal Information / Spinal Structure

Spinal Structure and Conditions Overview

* The data and diagrams in the section below are courtesy of: SpineUniverse.com and Spine-Health.com

1. Spinal Curves
    
   In the womb and for a period of time following birth, a baby's spine is shaped like the letter C. This curve is termed a primary curve, which is Kyphotic. During the time the baby is learning to lift his head and eventually walk, muscles develop. As muscular strength and ability is gained, the baby's activity will shift body weight to the spine. Gradually secondary curves develop in the cervical and lumbar regions; Lordotic curves. These curves will continue to develop until growing stops.
    

   Spinal curves are either kyphotic or lordotic. In a normal spine there are four types of spinal curvatures important to balance, flexibility, and stress absorption and distribution:   Type of Spinal Curve Kyphosis or Kyphotic Curve Lordosis or Lordotic Curve Curve Description Concave anteriorly and convex posteriorly Convex anteriorly and concave posteriorly Curvature Cervical Lordosis Thoracic Kyphosis Lumbar Lordosis Sacral Kyphosis Normal Curvature 20 to 40 degrees 20 to 40 degrees 40 to 60 degrees Sacrum fused in a kyphotic curve

    
    
2. Vertebral Column
    
   

   The spinal column (or vertebral column) extends from the skull to the pelvis and is made up of 33 individual bones termed vertebrae. The vertebrae are stacked on top of each other group into four regions:   The cervical spine is further divided into two parts, the upper cervical region (C1 and C2), and the lower cervical region (C3 through C7). C1 is termed the Atlas and C2 the Axis. The Occiput (CO), also known as the Occipital Bone, is a flat bone that forms the back of the head.

   Term Cervical Thoracic Lumbar Sacrum Coccyx number of Vertebraeb 7 (C1 - C7) 12 (T1 - T12) 5 or 6 (L1 - L5) 5 (fused) (S1 - S5) None Body Area Neck Chest Low Back Pelvis Tailbone

    
   

   The Atlas (C1) is the first cervical vertebra and therefore abbreviated C1. This vertebra supports the skull. Its appearance is different from the other spinal vertebrae. The atlas is a ring of bone made up of two lateral masses joined at the front and back by the anterior arch and the posterior arch.

   The Axis is the second cervical vertebra or C2. It is a blunt tooth-like process that projects upward. It is also referred to as the 'dens' (Latin for 'tooth') or odontoid process. The dens provide a type of pivot and collar allowing the head and atlas to rotate around the dens.
    
   

   The thoracic vertebrae increase in size from T1 through T12. They are characterized by small pedicles, long spinous processes, and relatively large intervertebral foramen (neural passageways), which result in less incidence of nerve compression.

   The rib cage is joined to the thoracic vertebrae. At T11 and T12, the ribs do not attach and are so are called "floating ribs." The thoracic spine's range of motion is limited due to the many rib/vertebrae connections and the long spinous processes.
    

   The lumbar vertebrae graduate in size from L1 through L5. These vertebrae bear much of the body's weight and related biomechanical stress. The pedicles are longer and wider than those in the thoracic spine. The spinous processes are horizontal and more squared in shape. The intervertebral foramen (neural passageways) is relatively large but nerve root compression is more common than in the thoracic spine.

   Although vertebrae range in size; cervical the smallest, lumbar the largest, vertebral bodies are the weight bearing structures of the spinal column. Upper body weight is distributed through the spine to the sacrum and pelvis. The natural curves in the spine, kyphotic and lordotic, provide resistance and elasticity in distributing body weight and axial loads sustained during movement.
    
   The vertebrae are composed of many elements that are critical to the overall function of the spine, which include the intervertebral discs and facet joints.
     
3. Facet Joints
    
   

   A joint is where two or more bones are joined. Joints allow motion (articulation). The joints in the spine are commonly called Facet Joints. Other names for these joints are Zygapophyseal or Apophyseal Joints.   Each vertebra has two sets of facet joints. One pair faces upward (superior articular facet) and one downward (inferior articular facet). There is one joint on each side (right and left). Facet joints are hinge-like and link vertebrae together. They are located at the back of the spine (posterior).

   Facet joints are synovial joints. This means each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. The joint surfaces are coated with cartilage allowing joints to move or glide smoothly (articulate) against each other.
    

   These joints allow flexion (bend forward), extension (bend backward), and twisting motion. Certain types of movement are restricted. The spine is made more stable due to the interlocking nature to adjacent vertebrae.