Herniated Nucleus Pulposus

Incidence of symptomatic disc herniation is 1–2% in the general population.

Most common age of presentation is during third and fourth decades of life.

Smoking leads to reduced O ₂ tension secondary to vasoconstriction, significant inhibition of cell proliferation and extracellular matrix synthesis, and increased abnormal type I collagen versus type II collagen overall, leading to disc degeneration.

Chronic stress (e.g., chronic coughing, sitting without lumbar support, heavy lifting) increases strain on disc.

Poor posture combined with poor body mechanics places stress on the lumbar spine and affects the distribution of body weight.

Obesity and largely sedentary lifestyle.

Structurally the lumbar disc has three components: the annulus fibrosus, forming the circumferential rim of the disc; the nucleus pulposus, composing its central core; and the cartilaginous end plates on the adjacent vertebral bodies.

The intervertebral disc is the largest avascular structure in the body.

The nucleus pulposus is composed of H ₂ O, collagen, and PGs. PG molecules are important because they attract and retain H ₂ O, constituting a hydrated gel-like matter that resists compression. The amount of H ₂ O in the nucleus varies throughout the day, depending on activity. It decreases with age, leading to degenerative disc disease.

The annulus fibrosus is an annular structure composed of concentric sheets of collagen fibers connected to the vertebral end plates. The sheets are oriented at various angles and enclose the nucleus pulposus.

Disc herniation occurs when the annulus fibrosus breaks open or cracks, allowing the nucleus pulposus to escape. This is called a HNP or herniated disc. Escaping material initiates an inflammatory reaction.

Disc herniation typically gives rise to radicular pain, which is pain in the distribution of the nerve root affected by the herniation. This pain has strong inflammatory and neuropathic components with or without neurologic change. If radicular changes take place, the presentation is that of a radiculopathy.

Lumbar region L4–L5 is most common site (59%), followed by L5–S1 (30%) and L3–L4 (9%).

Natural history of disease is favorable.

Most pts have substantial improvement of symptoms within a few mo.