An intervertebral disc is a fibro-cartilaginous joint between adjacent vertebrae. Like a shock absorber, it provides stability and at the same time dynamism to the entire vertebral column.
It is formed by a central part, called nucleus pulposus, made of almost 90% water, and an outer concentric ring called annulus fibrosus, which surrounds and contains the nucleus pulposus.
The posterior longitudinal ligament is a reinforcing structure. It extends from cervical to lumbar vertebrae, along the entire vertebral column, and covers the posterior surface of the annulus fibrosus and the vertebral bodies.
Nerve roots pass through the intervertebral foramina between one vertebra and the next. The nerve roots are the origin of the nerves that innervate their respective territories of competence.
Repeated stress exerted upon the spinal discs, bad postures, and handling heavy loads all lead to disc degeneration, which causes weakness of the annulus fibrosus and of its capacity to contain the nucleus pulposus.
Following a more or less intense stress, part of the nucleus pulposus can spill (through a tear created in the weakened annulus fibrosus) into the vertebral canal with the consequent compression of the spinal cord and / or of the nerve roots. This is the so-called spinal disc herniation.
Spinal Disc herniations are also classified, according to their location, as follows:
Intracanal herniation: when the nucleus pulposus spills into the spinal canal
Intraforaminal herniation: when the nucleus pulposus spills into the intervertebral foramina (that is, the "tunnel" through which the nerve roots pass to later innervate their respective territories)
Extraforaminal herniation: when the nucleus pulposus spills laterally to the intervertebral foramina
A further classification is based on the degree of spillage of the nucleus pulposus through the annulus fibrosa. It is referred to as:
Disc protrusion: when the annulus fibrosus goes through a deformation (but remains intact) caused by the nucleus pulposus
Contained Herniation: when the nucleus pulposus spills in the vertebral canal through a tear in the annulus fibrosus, but is still contained by the posterior longitudinal ligament.
Non-contained Herniation: when the nucleus pulposus detaches and spills through the posterior longitudinal ligament, reaching the vertebral canal without maintaining any relation of continuity with the spinal disc.
Usually, they are caused by excessive stress exerted on the spine, for instance due to:
Work activities that require physical efforts or poor posture
Strenuous sports activities
Genetic predisposition which causes some patients’ ligament containment structures to be more weary
Smoking (it damages the micro-circle of the disc structure and weakens it)
Disc herniations are more common in young adults, but they can occur at any age.
CERVICAL DISC HERNIATION
They affect the intervertebral discs interposed between the cervical vertebrae. They account for 25% of disc herniations.
The discs between C4 and C7 are most frequently affected by the development of Cervical disc herniation.
DORSAL DISC HERNIATION
They are the rarest kind (10%) and affect the discs interposed between the dorsal vertebrae, especially those between D8 and D11.
LUMBAR DISC HERNIATION
They are the most frequent kind (65%), as the lumbar region of the vertebral column is the one that supports most of the body weight, so the one that is most subjected to wear.
They mainly affect L4-L5 and L5-S1, also due to the smaller size of the posterior longitudinal ligament in this area, with a consequent lower containment capacity of the latter.