Back Anatomy

The spine is the central support of the body. It provides a framework to support the trunk and rigid protection for the spinal cord. The spine is made up of 24 segments called vertebrae. These bones are stacked on top of one another. There are seven vertebrae in the neck called cervical vertebrae. These are often referred to as C1 through C7 (top to bottom). The skull sits atop C1. The 12 vertebrae in the region of the chest are called thoracic vertebrae. From top to bottom, these are referred to as T1 through T12. Two ribs are connected to each thoracic vertebra, one on either side. All the ribs and thoracic vertebrae together form the thoracic cage which surrounds and protects the heart and lungs. The abdominal portion of the spine is formed by five lumbar vertebrae, referred to as L1 through L5. These vertebrae are much larger than those of the thoracic spine, which in turn are larger and stronger than the cervical vertebrae. The vertebrae increase in size from top to bottom to accommodate the increasing body weight. Below the lumbar spine is the sacrum, a large triangular shaped bone at the base of the spine forming part of the pelvis. The coccyx is the small bone at the end of the spine, and is also called the tailbone. When these curves are in their normal alignment, the body is in a balanced position.

The vertebrae are composed of several intricate parts. The vertebral body is a thin ring of dense cortical bone and is shaped like an hourglass, thinner in the center with thicker ends. The outer cortical bone extends above and below the superior and inferior ends of the vertebrae to form rims. The superior and inferior endplates are contained within these rims of bone. The pedicles are two short rounded processes that extend posteriorly from the lateral margin of the dorsal surface of the vertebral body. They are made of thick cortical bone and form part of the spinal canal. The laminae are two flattened plates of bone extending medially from the pedicles to form the posterior wall of the vertebral foramen or spinal canal. The pars interarticularis is a special region of the lamina between the superior and inferior articular processes. A fracture or congenital anomaly of the pars may result in a spondylolisthesis. The spinous process is the bone you can feel when running your hands down your back. The paired transverse processes are oriented 90 degrees to the spinous process and provide attachment for back muscles.

Facet Joints are joints between the bones in our spine which allow us to bend backward and forward and to twist and turn. There are four facet joints associated with each vertebra. A pair that face upward (superior articular facet) and another pair that face downward (inferior articular facet). These interlock with the adjacent vertebrae and provide stability to the spine. They allow the vertebrae to be linked like a chain and provide mobile connections between each vertebra. Like other joints in the body, the facet joints can be affected by arthritis.

Between vertebral bodies are small fibrocartilage cushions called intervertebral discs. The center, called the nucleus pulposus, is a soft white jelly like substance that provides most of the disc’s ability to absorb shock. The nucleus is held in place by the annulus fibrosus, a series of strong ligament rings that are connected to the vertebrae above and below each disc. The disc will compress when weight is put on it and spring back when weight is removed.

Discs do not have a supply of blood vessels to nourish them like other organs in the body. They depend on fluids rich with oxygen and nutrients passing back and forth from the bones above and below them. The fluid exchange depends on the difference of pressure between the inside of the discs and blood vessels in the bones around them. When the pressure drops inside the discs, fluids and nutrients rush in. This is why all disc nutrition and regeneration happens when we lie down and the pressure is taken off our discs. The mechanism is not very efficient, and as we age, the disc is exposed to wear and tear greater than its ability to heal and regenerate. The annulus layers become weaker and injuries, including degenerative disc disease, annular tears, disc bulging, disc herniation etc. can occur.

As will be shown later, the object of discal decompression utilizing the DRS program is to reduce the pressure inside the disc. This facilitates the transfer of fluids, nutrients and oxygen back inside the disc thus allowing its’ rejuvenation. Other benefits include the reduction of intradiscal pressure ( the pressure inside the disc), which results in the retraction of the bulging or herniated discs, relieving pressure on nerve structures. Tears in the disc annulus can be repaired, and as sufficient fluids and nutrients enter into the disc, degenerative disc disease can be halted and even improved. Rehydration of the disc nucleus restores disc height, relieving the pressure on inflamed facet joints. The DRS System is not just aimed at treating symptoms but is designed to alleviate the underlying problems that cause low back pain and facilitate the natural healing of the discs.

The spinal cord is part of the central nervous system of the human body. Throughout the length of the spine, 31 pairs of nerves branch off from the spinal cord and serve all parts of the body, transmitting sensory information to the brain, and information from the brain to the muscles. Movement of the body, bladder functions and sensory functions are all dependent on this information traveling up and down the spinal cord.

Each individual nerve root exits the spinal canal through a space called the neural foramen (or intervertebral foramen). In an adult the lower end of the spinal cord usually ends at approximately the first lumbar vertebra. The nerve roots that arise from the end of the spinal cord and continue down the spinal canal through the lower part of the spine looks like a "horse's tail" and are collectively named the cauda equina. Several different membranes enclose and nourish the spinal cord and surround the spinal cord itself. The outermost layer is called the "dura mater". The dura is a very tough membrane that encloses the brain and spinal cord and prevents cerebrospinal fluid from leaking out from the central nervous system. The space between the dura and the spinal canal is called the "epidural space". This space is filled with tissue, vessels and large veins. The epidural space is important in the treatment of low-back pain, because it is into this space that medications such as anesthetics and steroids are injected in order to alleviate pain and inflammation of the nerve roots.

The spinal canal is the anatomic casing for the spinal cord. The bones and ligaments of the spinal column are aligned in such a way to create a canal that provides protection and support for the spinal cord.

There are a series of ligaments that are important to the stability of the vertebral column Although ligaments will stretch to permit limited movement, they are rigid enough to maintain alignment of the spinal canal as it passes through each vertebrae. Important to the lumbar spine (lower back) are seven types of ligaments: The ligamentum flavum is a strong ligament that connects the laminae of the vertebrae. The term "flavum" is used to describe the yellow appearance of this ligament in its natural state. The ligamentum flavum serves to protect the neural elements and the spinal cord and stabilize the spine so that excessive motion between the vertebral bodies does not occur. It is the strongest of the spinal ligaments and often has a thinner middle section. Together with the laminae, it forms the posterior wall of the spinal canal. Anterior longitudinal ligaments and posterior longitudinal ligaments are associated with each joint between the vertebrae. The anterior longitudinal ligament runs along the front and outer surfaces of the vertebral bodies. The posterior longitudinal ligaments run within the vertebral canal along the back surface of the vertebral bodies. The interspinous ligament runs from the base of one spinous process (the projections at the back of each vertebra) to another. Intertransverse ligaments and supraspinous ligaments run along the tips of the spinous processes. Joint-related structures called capsular ligaments also play an important role in stabilization and movement.

The back is crisscrossed by broad bands of muscle. The widest muscles in the back are the trapezius, the levator scapula, the rhomboids, and the latissimus dorsi. The muscles in the lower back provide support for your upright posture. The muscles at the top of the back move the shoulders and arms, and help you breathe. Those in the central group steady the spine and enable you to bend forward and backward and to twist from side to side. The deeper muscles form an overlapping sheet that joins this central region to the phalanges on the scapula (shoulder blade) and pelvis (hips). Other muscles link these bones to the arms and legs. Many of the muscles that give strength to the back of the upper torso are near the surface of the skin. A deep layer of muscles, some interwoven with the ribs and others linked to the spine, provide flexibility and added stability to the back.

A group of back muscles called the erector spinae are an example of these muscles, which form on each side of the spine and consist of three columns. These muscles move the lower back, help straighten the back, provide resistance when a person is bending forward at the waist, and help a person return to the erect position.

The multifidus is another important muscle of the lumbar region. This muscle is thick and prominent in the lumbar spine and becomes smaller at its attachments high up the spine. It is an effective lever arm that allows the lumbar spine to bend backward. The interspinales muscles, located on either side of the interspinous ligament, also are active in the backward bending of the lumbar spine. The intertransversarii muscles attach to the transverse processes. These muscles are not only active in backward bending, but also in bending from side to side. The intersegmental muscles are a series of muscles near the bottom of the spine that connect one intervertebral segment to another. The small muscles deep in the back play an important role in controlling the joints between the vertebrae of the spine. They steady the spinal column so that the long muscles of the back can use the spine as a lever when bending and twisting the torso. These muscles are therefore, also important to posture. The abdominal muscles, located at the front and side of the abdomen, are very important in supporting and protecting the abdominal internal organs. They also play an important role in protecting movement of the vertebral column in backward bending, forward bending, and side bending.

The 24 vertebrae, 23 discs, 31 pairs of spinal nerves, 140 muscles that hook on to the vertebrae, plus ligaments, tendons and cartilage are all very complicated and are potential sources of back trouble. The low back area bears the most stress of movement and, therefore is usually the site of most problems.

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