The spine is comprised of bony vertebrae separated by discs. The neural structures of the spine include the spinal cord (T12-L1), The conus medullaris—which is the lower end of the spinal cord, and the Cauda Equina, which is the division of multiple nerve roots beginning at the level of L1. Conditions of the lumbar spine including disc herniation are a main cause of lower back pain.
The lumbar spine (lower back) consists of five vertebrae numbered L1-L5. These vertebrae are attached to the sacrum at the lower end of the spine. The discs between the vertebrae are round cushioning pads which act as shock absorbers. In a normal disc, there are two layers—the inner disc layer, which is comprised of soft gelatinous tissue and known as the Nucleus Pulposus, and the outer disc layer—which is made up of thick strong tissue, which is known as the Annulus Fibrosis. Behind this disc lies the spinal nerve root and the cauda equina. A major disc herniation of the lumbosacral region could affect the nerve roots.
In about 95% of all disc herniation cases, the L4-L5 or L5-S1 disc levels are involved. Herniation of the L4-L5 disc will affect the L5 nerve root. Herniation of the L5-S1 disc will affect the S1 nerve root.
There are three types of disc herniation:
- Protrusion/ Bulge- A bulging disc with intact annular and posterior longitudinal ligament fibers
- Disc Herniation
- Type A—Disruption of inner annular fibers with intact outer annular fibers
- Type B—Disrupted annulus with tail of disc material extending into the disc space
- Free fragment without tail extending into disc space
- Fragment may be reabsorbed spontaneously
- May get better with the use of an epidural
There are three typical locations for disc herniation as well:
- Involves multiple nerve roots
- Predominantly causes low back pain more than leg pain
- May cause incontinence of the bladder and bowel
- Urgent surgical treatment if patient presents with neurological deficits
- Posterolateral—usual location, most commonly involving one nerve root (the lower one)
- For example: L4-L5 posterolateral herniation will involve L5 nerve root
- Occurs in 8-10% of cases
- Involves the exiting nerve
- Example: L4-L5 foraminal herniation will involve the L4 nerve root
Discogenic Back Pain is an internal disc disruption with early disc degeneration. Pain gets worse with flexion and sitting but, gets slightly better with extension. Forward flexion is limited on the exam and there are no radicular symptoms.