Lumbar Spine (low back)

The lumbar spine is usually comprised of 5 individual bones of complex shape called vertebrae which have no ribs attached. (Occasionally, an individual is born with the lowest vertebra attached to the sacrum or the upper part of the sacrum separated as an "extra" vertabra which gives the appearance of 4 or 6 lumbar vertabrae.) The parts of the vertebrae called the "bodies" stack on top of each other creating a column which forms the front surface of the spine. Between the vertebrae are pads of cartilage called "intervertebral discs". Behind the main column, running the entire length of the spine is a tunnel for the spinal cord and nerves called the "spinal canal". The spinal cord actually ends in the upper portion of the lumbar spine and the canal below it contains only individual nerves which can tolerate being pushed around more easily than the cord. All this is surrounded by bone structure which has gaps from one segment to the next. Each segment of this structure attaches to a single vertebral body. Each segment has a portion called the lamina which forms most of the back wall of this spinal canal and there is a ligament filling the gaps between the laminae from one segment to the next. Also, there are joints called "facets" formed by the contact of special surfaces on the upper and lower faces of each segment and on both sides of the canal. A single facet joint is made of the upper surface from one segment and the lower surface of another segment. Some sliding movement between the surfaces at each joint is expected to permit a limited degree of spinal mobility. The intervertebral discs are just supposed to flex or twist a little during movements.


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