Spinal Anatomy 101

	This is a representation of a lumbar vertebra.   On the right-side of both sketches is the vertebral body.   On the left-side of both views is the ring of bone (called the lamina) which houses the spinal cord. At the front of each lamina is a column of bone called the pedicle.   On the top and bottom of each pedicle are found the facet joints (zygapophyseal or “Z joints”) which permit the normal motion of the vertebra...flexion, extension, rotation, and lateral bending.
	The “Spinal Motion Unit” Two vertebra, and the tissues that connect then, comprise the smallest working unit of the spine. This unit is referred to as the “spinal motion unit”. This motion unit (shown on the left) demonstrates normal flexion and extension. You will also notice that the only motion that takes place at the vertebral disc (IVD) is compression at the front of the disc (during flexion), and at the back of the disc (during extension).   There should be no forward or backward motion of the vertebral bodies (also known as as translation) when the integrity of the IVD is intact. See the hole directly behind the blue disc?   This is the intervertebral foramina (IVF) and this is where the spinal nerve roots pass from the spinal cord, out to the body.   When the vertebra flexes, the facets slide upwards and forwards, and the size of IVF increases. In extension, the size of the IVF decreases.
	Nerve Root Impingement The facet complex is located directly behind the IVF. If there is inflammation at the facets, the swelling of the joint capsule can encroach on the IVF, impinge upon the nerve roots, and cause nerve root irritation (also known as “radiculopathy”). This picture demonstrates nerve root impingement caused by a herniated disc. The typical symptoms of radiculopathy include pain, tingling or numbness (“paresthesia”), and muscle weakness along the distribution of that nerve root.
	This sketch shows the nerve root exiting the IVF, and perhaps makes it easier to visualize how inflammation, either at the facet joints or the disc, can encroach upon the delicate nerve roots.

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Since 5-16-2007

Updated 2-19-2008