Thursday, December 16, 2010
Anatomy of the Low Back
Several key structures make up the low back: lumbar vertebrae L1-5; intervertebral discs that separate the lumbar vertebrae; the sacrum; and myofascial structures such as the psoas, diaphragm, and the abdominal viscera. Tension or imbalance in any of those structures can predispose someone to low back pain and/or injury, or cause pain in itself.
Lumbar Vertebrae, Discs, and the Spinal Cord
As you can see, the spinal cord runs through the spinal canal of each vertebra, sending out nerve roots at each level. Intervertebral discs act as spacers between the vertebra and allow for fluid movement of the spine. Damage to the discs--as a result of injury or long-term imbalance--sometimes causes part of the disc to bulge out and impinge on a spinal nerve root.
This unfortunate circumstance is, in my opinion, often the end result of a long-term imbalance, sometimes compounded by a triggering event (a fall, a lifting-and-twisting motion), but sometimes not. The source(s) of imbalance can often be found in the myofascial structures. If addressed early, the spine can restore balance and become more resilient, more resistant to injuries of this kind.
Myofascia of the Low Back
A few myofascial structures attach directly to the lumbar vertebrae: the respiratory diaphragm (via the crura, or “legs”, which connect the diaphragm to the lumbars,) the psoas, and the posterior portion of the peritoneum (visceral bag), which supports the large and small intestines.
Inflammation in the intestines, which leads to restriction in the peritoneum, may also influence movement (or its lack) in the lumbars.
The sacrum, as the bottom of the spine, plays a crucial role in the balance of the spine as a whole. It acts as a counterbalance to the head, it is the touchstone of the pelvis, and it is through it that the motion of the legs translates up into the spine.
Some individuals have natural torsions in their spines and sacra and experience no ill effects from them. Others have less functional torsions that cause all manner of back and hip pain.
Any sacrum that finds itself in a position that is greatly abnormal relative to its usual will cause some kind of pain, very often in the low back. The triggering event may be major or minor (landing on one’s rear end, moving a heavy object, etc.) but the end result is a rotated and tilted sacrum.
In the interest of brevity, I have not made this an exhaustive anatomical list. There are many other ligamentous and myofascial structures that, when damaged or strained, can cause significant pain and dysfunction in the low back. I have merely attempted to highlight a few of the more interesting ones from a bodywork perspective, and attempted to shed some light on a common source of discomfort.