The spine consists of a series of joints which are united from the second cervical to the first sacral by a number of ligaments. The vertebral bodies are united by anterior and posterior ligaments, and the posterior series of facet joints and neural arches are united by the ligamentum flavum. The function of these and other ligaments is to hold the bone together and yet allow some calculated movements.
The ligaments are elastic structures with an elastic limit. They remain healthy with intermittent stretching. Ligaments can be torn in two ways: sudden force and uninterrupted prolonged moderate stretching. This is why intermitted traction is more physiological than continuous sustained traction.
Anterior Longitudinal Ligament
A long and strong fibrous ligament runs on the anterior surface of the vertebrae. It is attached firmly to the disc and margins of the vertebral body, and loosely attached to the middle part of the body. It is wider at the level of the disc and narrower at the level of the body. A tear in any of the ligament fibres leads to haemorrhage, oedema and fibrin formation.
If given sufficient time, the ligament becomes as strong as before, but if stretched too soon, it remains weak and repair is incomplete. The ligament may get elongated, making the joint hypermobile. When stretched continuously for prolonged periods, the ligament starts aching and its elasticity gets diminished.
Posterior Longitudinal Ligament
The posterior longitudinal ligament is attached to the posterior margin of the vertebral body within the vertebral canal. It forms a bridge over the body of the vertebrae and is attached firmly to the intervertebral disc and to the margins of the vertebral body. Thus it reinforces the disc posteriorly. This ligament plays an important role in disc protrusion.
The resistance of the ligament helps to push the protrusion back again. The constant occurrance of lumbago in some persons may be caused because the protrusion is enlarged and pushed to the area of lesser resistance, thus producing unilateral sciatica pain. It is due to the posterior longitudinal ligament rupturing so completely, backwards and thus the cauda equina (lowermost roots of the spinal chord) is subjected to great pressure which may result in bilateral sciatica.