Anatomy of the spine

The spine is an interconnected complex of bones, nerves, muscles, tendons, and ligaments, any of which can become damaged and cause pain, neurological symptoms, or loss of mobility. Vertebrae are the bony building blocks of the spine. There are seven cervical vertebrae in the neck, twelve thoracic vertebrae in the upper back, and five lumbar vertebrae in the lower back. Each vertebral segment consists of a cylinder-shaped bone at the front of the spine, called the vertebral body, a soft cartilage disc between each vertebra, and paired facet joints at the back. Each segment is named after the vertebra above and below it, such as the C6-C7 segment. The bones of the spine surround and protect the spinal cord, which runs behind the vertebral bodies in a canal from the neck down to the top of the lumbar spine. In the lumbar spine, nerves branch out of the spinal canal and exit the spine in a horse-tail-like pattern, called the cauda equina. At each segment, spinal nerve roots exit the spine through holes in the back of the vertebrae called foramina. Any compression of a nerve root at the vermiform foramen, which can occur from bone spurs, herniated or degenerative discs, or facet joint problems, can cause pain and possible neurological symptoms to radiate along the nerve's path. These conditions are commonly called radiculopathy, and leg symptoms may also be called sciatica. Between the vertebrae, intervertebral discs act as shock absorbers and help to facilitate movement of the spine. These discs can degenerate over time and become a source of pain, a condition called degenerative disc disease. The soft inner core of the disc can get in the way, called a herniated disc, and irritate a nearby nerve root. The pain radiates along the path of the affected nerve and into the arm or leg. The sacrum connects the base of the spine to the pelvis at the sacroiliac joints. If these joints are too loose or too tight, it can cause low back pain due to dysfunction in the sacroiliac joint. Below the sacrum is the coccyx, or tailbone, which is made up of several small bones. Any damage to this area can cause tailbone pain. The entire spine is knitted together by a series of interconnected ligaments and tendons that help support and stabilize the spine while providing great flexibility.