The spinal column is formed by a series of pieces (the vertebrae) that fit together and articulate, in the absence of deformity, harmoniously with each other in the young stages of life.
This human axis consists of 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae and continues with the sacral vertebrae. In its interior is the vertebral canal, where the spinal cord is located, from which emerge the different nerves that coordinate the movement and sensibility of the different extremities.
All this set is protected by a powerful ligamentary structure that confers stability while allowing movement.
The muscular structure that surrounds this entire axis, in addition to protecting, contributes to ensure the posture and dynamics of the spine, allowing the mobility of the spine when performing movements such as extension, lateral tilt and flexion, being also important in the generation of strength necessary to perform various essential activities in daily life.
Between the aforementioned vertebral pieces, the intervertebral disc sits and acts as a cushion between vertebrae, distributing the different pressures or biomechanical loads to which the intervertebral disc is subjected.
As life progresses, and influenced by congenital, structural, environmental, occupational and age factors, a progressive wear and tear is produced either by overuse or misuse.
What is the composition and what is the function of the intervertebral disc that makes it so important?
The intervertebral disc is composed mostly of collagen, proteoglycans and water. The great strength of the disc is due to its water content, which reaches values of 70-90%.
Structurally, it has two fundamental components, the nucleus pulposus in the center and the annulus fibrosus in the periphery. A third structure, the cartilaginous plates cover the upper and lower surface of the disc and adhere to the vertebral bodies. The nucleus supports 75% of the load on the spine and the annulus 25%.
The function of the disc is to allow mobility between the different vertebral bodies and to transmit loads. Its structure allows it the capacity to absorb and disperse forces to which the spine is subjected.
What exactly is a herniated disc?
A herniated disc is a consequence of the alteration of the intervertebral disc that occurs when there is a tear/rupture of the annulus fibrosus (external part of the disc) and consequent protrusion/extrusion of the nucleus pulposus (the internal part of the disc) generating a conflict of space with the adjacent neural structures, usually a compromised lumbar root, causing the usual characteristic sciatica.
Why do herniated discs usually develop and are there factors that may influence their appearance?
Basically, herniated discs may be due to acute, punctual overexertion, to repeated sustained microtraumas and predominantly to degenerative phenomena.
There are structural and biomechanical factors that influence the vulnerability of the intervertebral disc.
The structure of the intervertebral disc is not perfectly designed to resist the lateral tilt, rotation or shear forces to which it is subjected, so that the posterior portion of the annulus is weakened by multiple subclinical events that eventually result in an acute herniation produced by a compressive flexion-rotational force.
The degeneration of an intervertebral disc is the product of a generalized process and is associated with biochemical, cellular and morphological changes.
The vascularization of the intervertebral disc progressively decreases in the first decades of life, changing its vascular nutrition system to an osmotic system.
Progressive dehydration reduces the load absorbing and load sharing function of the disc.
In addition, recognized factors that predispose to disc degeneration and therefore may influence the onset of disc herniation include:
- Maintained overweight/obesity
- Work activities involving high traction
- Heavy loads or lifting of heavy weights
- Vibration platforms
- Driving motorized vehicles
- Sedentary lifestyle
- Increased lumbar lordosis
- Loss of abdominal tone
- Psychological stress
- Persistent cough
- Chronic bronchitis characteristic of smokers (either by coughing or by decreased blood flow to the vertebral body affecting disc metabolism and making it more susceptible to mechanical deformities).
What symptoms may lead to suspect a herniated disc and not another spinal pathology?
The changes in the intervertebral disc (fragmentation and intradiscal fissures) that precede established disc herniation are in many cases asymptomatic, since the interior of the disc hardly receives any innervation. Low back pain appears when the annulus fibrosus is affected.
When the disc herniates, the pressure received by the annulus is transferred to the nerve root causing the radicular pain characteristic of sciatica. When the annulus ruptures completely and the intradiscal fragment invades the spinal canal, low back pain and stiffness improve but sciatica intensifies.
Therefore, the fundamental symptom that will make us suspect a disc herniation is sciatica, which is an acute pain radiating from the buttock and progressing towards the thigh, leg and even the foot. It may be preceded by intermittent episodes of low back pain. Sometimes it starts suddenly after a sneeze or coughing episode.
It usually worsens when we are seated and improves when standing or lying down. It is frequently accompanied by sensory alterations, tingling or a cramping sensation in the leg or foot, generally depending on the root involved.
When the picture persists over time or the nervous conflict is important, muscle weakness or loss of strength appears, with difficulty to walk normally or sensation of leg or foot failure.