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Why is the Disc Important?
The disc is a functional center component of the "three-joint complex" and the main support structure of the spine (disc and two facet joints).
These fibro cartilaginous pads that separate the vertebrae serve as a kind of hydraulic system by absorbing mechanical shock and compressive forces. The facet joints absorb some of the forces and they also protect the discs by limiting spinal rotation and shear forces.
The discs are composed of a viscous gel-like material in the center called the nucleus pulposus surrounded by layered rings of a fibrous material called the annulus fibrosus. The discs are bordered on top and bottom by the vertebral endplates that are normally porous and allow fluid and nutrients to pass from the vertebrae into the disc.
What is Intervertebral Disc Disease?
There are two major conditions that affect the discs of the spine: degenerative disc disease and disc herniation. Disc herniation is considered more episodic or acute and degenerative disc disease is more ongoing or chronic.
Disc herniations are classed in terms of degree of migration of the nucleus from the middle outward through ruptures in the annulus. The resultant bulge of protrusion may place pressure directly on nerve roots causing pain or damage to nerves. The most susceptible location for this condition is in the lumbar spine between the 4th and 5th lumbar vertebra. Most vulnerable to this condition are adult males between 30 and 40. Normally the discs provide cushioning between the vertebrae but are vulnerable to injury through abnormal spinal motion combined with excessive axial loads.
What are the Causes of Intervertebral Disc Disease?
Degenerative and biochemical changes from mechanical insult (such as sitting, bending, lifting) and aging tend to compromise the hydraulic capacity of the disc. With a breakdown of nuclear material compressive loads on the spine are not well tolerated. The endplates may fracture and spinal loads may be transferred to the facet joints.
Because of the dynamic nature of the motion segments that make up the spine any alteration in function of one component of this hydraulic system will tend to have adverse consequences on other supporting structures.
What are the Symptoms of Intervertebral Disc Disease?
Pain patterns associated with disc herniation involve irritation down the course of the irritated nerve including tingling and numbness down the back of the leg in the case of lumbar (low back) involvement and similar symptoms into the arms and hands in the case of cervical (neck) involvement.
In the degenerated disc we see a progressive breakdown of the normal structure characterized by dehydration combined with tears in the annular tissues. The result will be a decrease in the normal disc height. If the affected disc is in the lumbar spine it will tend to cause low back pain. The pain is similar to osteoarthritis -like symptoms and tends to be achy and dull in nature except when there is an acute flare-up of the condition. In this case the symptoms are similar to disc herniation in which the pain may radiate away from the site of the involved disc.
How is Intervertebral Disc Disease Prevented or Treated?
Disc disease tends to be resistant to recovery due to the poor blood supply of the disc. For that reason it is desirable to adhere to a lifestyle that protects the discs and the spine in general. Exercises and spinal rehabilitation serve to increase the functional capacity, flexibility and strength of the spine. Stabilization and strengthening exercises serve to prevent disc disease but are also used as an alternative to surgery.
1) Brier, Steven R. Primary Care Orthopedics. St. Louis: Mosby, Inc., 1999
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