The spine is composed of 33 individual vertebrae. This spinal column provides the main support to maintain the body up straight and allows movement in several planes while protecting the spinal cord from injury. Strong bones and muscles, flexible tendons and ligaments, and sensitive nerves contribute to a healthy spine. Yet, any of these structures affected by strain, injury, or disease can cause pain.
Vertebrae are consisted of 33 individual bones that interlock with each other to form the spinal column. The vertebrae are numbered and divided into regions: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal (Fig 1. Spine). Only the top 24 bones are moveable whereas the vertebrae of the sacrum and coccyx are fused.
Cervical region – the main function of the cervical spine is to support the weight of the head (about 10 pounds). The seven cervical vertebrae are numbered C1 to C7. The cervical region has the greatest range of motion because of two specialized vertebrae that connect to the skull. The first vertebra (C1) is the ring-shaped atlas that connects directly to the skull. This joint allows for the nodding or “yes” motion of the head. The second vertebra (C2) is the peg-shaped axis, which has a special projection called the odontoid process, that the atlas pivots around. This joint allows for the side-to-side or “no” motion of the head.
Thoracic region –the main function of the thoracic spine is to protect the organs of the chest by providing attachment for the rib cage. The 12 thoracic vertebrae are numbered T1 to T12. The range of motion in the thoracic spine is limited.
Lumbar region –the main function of the lumbar spine is to bear the weight of the body. The five lumbar vertebrae are numbered L1 to L5. These vertebrae are much larger in size for their weight-bearing function.
Sacral region –the main function of the sacrum is to provide attachment for the iliac (hip) bones and protect the pelvic organs. There are five sacral vertebrae, which are fused together. Together with the iliac bones, they form a ring called the pelvic girdle.
Coccyx region –the four fused bones of the coccyx or tailbone don’t really have a function. It is an embryology remnant of a tail from our primate ancestors.
The facet joints of the spine allow back motion. Each vertebra has hour joints, one pair that connects to the vertebra above (superior facets) and one pair that connects to the vertebra below (inferior facets). (Figure 3. Facet joints)
It is very important to understand about the joint line in each facet joints while performing Mulligan technique on the spine, in order to apply a correct and effective gliding or distraction force. Vertebrae are interlock with each other to form the spinal column. Within this interlocked vertebrae, the facet joints take important roll in guiding and limiting movement of the spinal motion segment. Each vertebrae’s facet joint has their own unique shape and because of this unique shape, each facet joint provides different joint line. (Figure 4. Joint lines)
In order to apply the correct and effective joint mobilization technique the gliding force has to be parallel to the red lines in the figure 4.
[Most of theliteratures were taken from http://www.mayfieldclinic.com/PE-AnatSpine.htm]