The spine is the central column of the human body. It not only provides the primary skeletal structure from which the limb and torso bones emanate, but it also houses the spinal cord, which is an extension of the central nervous system and enables the brain to send signals to the rest of the body. Because people move upright, the length of the spine needs to be incredibly strong and flexible in order to absorb the different changes in direction, speed and motion that people make in their movement all the time, as well as to support the bulk of the human body, which effectively hangs from this column. The ligaments in the spine offer significant support to the spinal column by joining vertebra to vertebra over and around the intervertebral tissues and providing a casing to protect this fragile yet crucial skeletal organ. Here is an overview of these ligaments, their location and function.
There are three major ligaments that run longitudinally along the spine from the base of the skull to the sacral area at the base of the spine. Between each individual vertebra are the minor ligaments which work to create stability between the spinous processes.
-Anterior Longitudinal Ligament (ALL)
This ligament runs from the base of the skull to the end of the spine and is located along the anterior or front surface of the spine. The ALL also joins the forward aspects of the vertebrae to the forward aspects of the annulus fibrosis, which are the discs in between each vertebra. It is known as a primary spine stabiliser and is the stronger of the two longitudinal ligaments which run parallel down the spine.
-Posterior Longitudinal Ligament (PLL)
The PLL, whilst also known as a primary spine stabiliser, is the weaker ligament, located parallel to the ALL on the posterior or rear side of the length of the spine. The PLL joins the posterior aspects of the vertebrae to the posterior aspects of the annulus fibrosis.
This ligament is the strongest of the major ligaments in the spine. It runs down the spine from the base of the skull to the pelvis and is located as a covering around the length of the dura mater (the outer covering of the spinal cord), which is found inside the space between the vertebrae and the spinous processes. The ligamentum flavum protects the spinal cord and also is connected to the laminae and runs in front of the facet joint capsules, ensuring that even these tiny areas are supported and strengthened.
These small ligaments run between each adjacent spinous process at different points. The supraspinous ligaments attach the outer ends of the spinous processes to each other. The interspinous ligaments are found between the inner areas of the spinous processes as a thinner tissue, and also attach onto the ligamentum flavum. These ligaments ensure that each vertebra remains in place, whilst still allowing for flexion between the spinous processes, which enables the spine to bend from side to side safely.
The function of ligaments in all areas of the skeletal structure are to join bone to bone, thus offering a range of movement within safe parameters. In the case of the spine, which is a complex area, the ligaments also function to protect the spinal cord and the soft discs in between the vertebrae, so that movement of the body does not throw any bone out of place, which would threaten the spinal cord and the other soft tissue in the spine. Since all movement affects the spinal column, the importance of these ligaments cannot be overstated, regardless of the categorisation as 'major' or 'minor', as they are each as necessary as the other for the effective motion of the body as a whole.