Anatomy of the Spine
The Spinal Column/Vertebrae
The spinal column is made up of 33 bones, called vertebrae, that stack one on top of another with intervertebral discs between and connecting at the facet joints. The spinal column supports the loads of the upper body, serves as an attachment point for muscles and ligaments that provide constrained motion and protects the spinal cord. There are five regions of the spine:
- The top seven vertebrae make up the cervical (or neck) resion;
- The next 12 vertebrae are attached to the ribs and make up the thoracic (or chest) region;
- The next five vertebrae support most of the weight of the torso and make up the lumbar (or lower back) region;
- The next five vertebrae are fused into one bone called the sacrum;
- And the final four vertebrae are fused to make up the small coccyx (or tail-bone).
Each of the vertebrae in the spinal column is separated by an intervertebral disc (except the fused bones of the sacrum and coccyx). These discs are made up of a tough, elastic outer ring of collagen fibers (annulus) surrounding a soft gel center (nucleus). The discs cushion the spine during loading and bending activities. The aging process naturally causes the discs to lose water over time; this is known as the degenerative process. Degenerated discs don't cushion the spine as well as normal discs, which can lead to disc herniation, pain and instability.
Ligaments are tough bands of elastic tissue that connect bones together and help to restrain excessive motion at the joints. The spinal ligaments help to stabilize the spinal column during motion.
The shape of the vertebrae allows for the passage of the spinal cord from the brain to the lower part of the body through the spinal canal. Spinal nerves stem from the spinal cord and exit the spinal column between each vertebrae on both sides. The spinal cord ends at the upper lumbar region, below which is a bundle of spinal nerves called cauda equina. After exiting the spinal canal, these spinal nerves then further entwine and extend to send signals between your brain and your organs. The muscles, and other tissues. The lumbar spinal nerves innervate your lower back, abdomen, and legs. If any of these nerves are pinched by a bulging disc or the position of your vertebrae you might experience back, groin, and/ or leg pain or numbness.
Back and Trunk Muscles
The spinal stabilizers are the muscles that attach to it. The paraspinal muscles that run up and down the center of the back are those which are sometimes painful, both before, and often after surgery (from the surgical approach). Minimally disruptive surgical procedure attempt to minimize this approach-related muscle pain. The XLIF® procedure, specifically, avoids muscle pain almost entirely by approaching the spine from the side rather than from the back. The side trunk muscles (abdominal oblique muscles) are more forgiving, and approaching from here will allow less painful postoperative recovery. Under these oblique muscles is a space between the abdomen and the back muscles called the retroperitoneal space. At the bottom of this space lies the psoas muscle, covering the sides of the vertebrae. This muscle helps you to bend at the hip. It is through this space and through this muscles that the surgeon will reach your spine. The spinal nerves that exit the spine and travel to the legs through the psoas muscle (lumbar plexus) will be monitored throughout the surgery using EMG nerve avoidance technology (NeuroVision®).