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An estimated 4.1 million Americans had symptoms of an intervertebral disk disorder between 1985 and 1988, and, of those, as many as 60 percent of men 45 years or older reported having sciatica. Sciatica leads to surgery more often than does back pain alone.
Intervertebral disks lie between the bones of the spine (vertebrae), and function as shock absorbing cushions between the vertebrae. Every time you walk, run, bend, lift, twist (etc), force travels to and through the spine. The spine’s function is to protect the delicate spinal cord, the large nerve which functions as the main “cable of communication” from the brain to the rest of your body. [15,16]
The disks are round, doughnut-like structures that have two pieces: a tough, outer ring (annulus fibrosus) that contains a soft center (nucleus pulposus) with a high water content, about the consistency of toothpaste. Spinal injury and/or wear and tear (twisting, flexing, extending, repeated loading) may cause the outer ring to tear. When this occurs, the soft center “pop outs” or “herniates” through the tough outer ring. Because the soft, toothpaste-like nucleus pulposus is not supposed to be outside of the ring, it produces inflammation in the area of either the spinal cord or nerve roots, which irritates these nerves.
If you look at the diagram above, you can see that the spine has a canal in the center where the spinal cord is. The spinal canal and cord are in the center of the spine. Additionally, there are holes toward the back and sides of the vertebral bones, where nerve roots leave to connect the spinal cord/brain to the rest of the body. For example, some nerve roots travel to legs/foot to signal them to move, others sense pain. This aspect of the spine faces toward the sides/back of the body.
When the disk ring partially tears, the soft nucleus pops out either toward the center (the spinal cord) or toward the back/sides (the nerve roots). Disk herniation producing nerve root irritation is one way sciatica occurs. Much less commonly, the disk herniates toward the center/spinal cord, producing problems with leg movement or, rarely, cauda equina syndrome (see below). Even less commonly, the disk’s outer ring acutely and completely ruptures, requiring immediate surgery (disk rupture).
Normal, healthy disks do not sense pain, as they do not have pain-sensing nerves in them. However, badly damaged disks do obtain these these “pain sensors” over time (this also occurs with degenerative disk disease). Therefore, healthy, torn disks do not produce pain; it is the disk material and its associated inflammation that signal pain. As a result, most disk herniations will respond/resolve with time and/or physical therapy to help stabilize the spine and prevent recurrence. Conventional therapy also includes non-steroidal anti-inflammatories, anti-inflammatory steroids, narcotics, muscle relaxants, epidural injections with steroid, and occasionally surgery (microdiskectomy or diskectomy with laminectomy).
The rare, significant, sudden form of central disk herniation called cauda equina syndrome, commonly produces pain in one leg, paralysis of the legs (without spasticity), bowel and bladder changes (incontinence or retention), as well as “saddle anesthesia:” a numbness or tingling in the crotch area that may extend to the interior of the upper thighs. There is weakness when transferring from sitting to standing and with heel/toe walking. This is an urgent condition and must be immediately evaluated by a surgeon.
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