THE LUMBAR VERTEBRAE
The vertebrae are the individual building blocks of the spine. Each has a front and back compartment. The front compartment consists of the circular vertebral body, shaped like a cotton reel, which is specifically designed to stack easily and bear weight.
The back compartment protects the spinal segments together so they stay in place.Five lumbar vertebrae make up the low back. At the base of the spine the bottom vertebrae (L5) sits on the sacrum and the junction between the two is called the lumbo-sacral or L5-S1 joint. As the most compressed level in the spine it is the most problematic. Nearly all back pain comes from dysfunction of the front or back compartment (sometimes both) at this level.The back compartment is a ring of bone extending backwards from the vertebral body which barely takes weight. In standing it bears takes weight.
In standing it bears approximately 16 percent of body weight, but less if the spine is more humped in the sitting position where the facets are less engaged. With severe disc narrowing-the primary form of breakdown of the spine-the facets may be forced to take much more weight (upto 70 percent of the weight through the spine), which is tremendously destructive.
Each ring of the back compartment has small projections of bone sprigging from the outside corners: two wings out either side, called the transverse processes and a fin projecting out the back called the spinous process (these are the knobs of the spine running down the back you can see through the skin). All these bony bars serve as levers for the attachment of muscle which make the vertebrae move.All the muscles working the segments exert a downward pull as they make them move.
This is noteworthy because lumbar compression is the main cause of low back pain. If you bear in mind how much time we spend upright, fighting the weighing-down effects of gravity, you can see there are two factors at the start-our weight and the muscular strings moving the vertebrae-contributing to compression caused by sitting.The cotton reels superimposed on one another at the disc-vertebrae union make up the beautifully bendable neurocentral core, and the junctions between are often called the inter body joints.
The bony inter-notching either side at the back makes a chain of mobile juicy aphophyseal or facet joints, running down the entire length of the spine. Together, the two different types of joints of the front and back compartment make up the total ‘motion segment’ at each spinal level.
The vertebrae are prevented from grinding on one other by the intervertebral discs. These are high pressure fibrous sacks containing a central unsquashable sphere of mucoid fluid called a nucleus. The long column of bones with its high-tensile fibro-elastic pillows makes the neuro centralcore thrusting and resilient, able to take nearly all of the weight passing down through the body.
The actual shape of the bodies of the vertebral helps spread the load. They have a narrow waist which flares out to a broad weight-bearing upper and lower surface. Unlike the other lumbar vertebrae, L5 is thinner at the back which helps to form the lumbar lordosis. Its disc is also slightly wedge-shaped although it is still the fattest disc in the spine, helping it to bear the load of the rest of the spine on top.