The spine is one of the most important parts of your body. Without it, you could not keep yourself upright or even stand up. It gives your body structure and support. It allows you to move about freely and to bend with flexibility.
The spine is also designed to protect your spinal cord. The spinal cord is a column of nerves that connects your brain with the rest of your body, allowing you to control your movements. Without a spinal cord, you could not move any part of your body, and your organs could not function. This is why keeping your spine healthy is vital if you want to live an active life.
ANATOMY OF THE SPINE
What exactly is the spine? Your spine is made up of 24 small bones (vertebrae) that are stacked on top of each other to create the spinal column. Between each vertebra is a soft, gel-like cushion called a disc that helps absorb pressure and keeps the bones from rubbing against each other. Each vertebra is held to the others by groups of ligaments. Ligaments connect bones to bones; tendons connect muscles to bones. There are also tendons that fasten muscles to the vertebrae. The spinal column also has real joints (just like the knee or elbow or any other joints) called facet joints. The facet joints link the vertebrae together and give them the flexibility to move against each other.
Each vertebra has a hole in the center, so when they stack on top of each other they form a hollow tube that holds and protects the entire spinal cord and its nerve roots. The spinal cord itself is a large collection of nerve tissue that carries messages from your brain to the rest of your body. The spine branches off into thirty-one pairs of nerve roots. These roots exit the spine on both sides through spaces (neural foramina) between each vertebra.
The spine itself has three main segments: the cervical spine, the thoracic spine, and the lumbar spine. The cervical is the upper part of the spine, made up of seven vertebrae. The thoracic is the center portion of the spine, consisting of 12 vertebrae. The lower portion of the spine is called the lumbar spine. It is usually made up of five vertebrae, however, some people may have six lumbar vertebrae. Having six vertebrae does not seem to cause a problem. Below the lumbar spine is the sacrum. The sacrum is actually a group of specialized vertebrae that connects the spine to the pelvis. The nerves that leave the spine in the sacral region control the bowel and bladder functions and give sensation (feeling) to the crotch area.
The normal spine has an “S”-like curve when looking at it from the side. This allows for an even distribution of weight. The “S” curve helps a healthy spine withstand all kinds of stress. The cervical spine curves slightly inward, the thoracic curves outward, and the lumbar curves inward. Even though the lower portion of your spine holds most of the body’s weight, each segment relies upon the strength of the others to function properly.
Back specialists sometimes look at a spinal segment to understand and explain how the whole spine works.
A spinal segment is made up of two vertebrae attached together by ligaments, with a soft disc separating them. The facet joints fit between the two vertebrae, allowing for movement, and the neural foramen between the vertebrae allow space for the nerve roots to travel freely from the spinal cord to the body.
The spinal segment allows us to focus on the repeating parts of the spinal column to better understand what can go wrong with the various parts of the spine. Sometimes problems in the spine involve only one spinal segment, while other times the problems involve multiple segments.
Each spinal segment is like a well-tuned part of a machine. All of the parts should work together to allow weight bearing, movement, and support. When all the parts are functioning properly, all spinal segments join to make up a remarkably strong structure called the spinal column. When one segment deteriorates to the point of instability, it can lead to problems at that segment causing pain and other difficulties.
MAIN SPINAL ELEMENTS
The spine has three main segments: the cervical spine, the thoracic spine, and the lumbar spine. The sacrum is actually a group of specialized vertebrae that connects the spine to the pelvis.
The cervical spine is made up of the first seven vertebrae in the spine. It starts just below the skull and ends just above the thoracic spine. The cervical spine has a lordotic curve (a backward “C”-shape) - just like the lumbar spine. The cervical spine is much more mobile than both of the other spinal regions - think about all the directions and angles you can turn your neck.
Unlike the rest of the spine, there are special openings in each vertebra in the cervical spine for the arteries (blood vessels that carry blood away from the heart), as well as the spinal canal that carries the spinal cord. The arteries that run through these openings bring blood to the brain.
Two vertebrae in the cervical spine, the atlas and the axis, differ from the other vertebrae because they are designed specifically for rotation. These two vertebrae are what allow your neck to rotate in so many directions, including looking to the side.
The atlas is the first cervical vertebra - the one that sits between the skull and the rest of spine. The atlas does not have a vertebral body, but does have a thick forward (anterior) arch and a thin back (posterior) arch, with two prominent sideways masses.
The atlas sits on top of the second cervical vertebra - the axis. The axis has a bony knob called the odontoid process that sticks up through the hole in the atlas. It is this special arrangement that allows the head to turn from side to side as far as it can. Special ligaments between these two vertebrae allow a great deal of rotation to occur between the two bones.
Though the cervical spine is very flexible, it is also very much at risk for injury from strong, sudden movements, such as whiplash-type injuries. This high risk of harm is due to: the limited muscle support that exists in the cervical area, and because this part of the spine has to support the weight of the head. This is a lot of weight for a small, thin set of bones and soft tissues to bear. Therefore, sudden, strong head movement can cause damage.
The thoracic spine is made up of the middle 12 vertebra of the spine. These vertebrae connect to your ribs and form part of the back wall of the thorax (the ribcage area between the neck and the diaphragm). This part of the spine has very narrow, thin intervertebral discs, so there is much less movement allowed between vertebrae than in the lumbar or cervical parts of the spine. It also has less space in the spinal canal for the nerves.
The thoracic spine’s curve is called kyphotic because of its shape, which is a regular “C”-shaped curve with the opening of the “C” in the front.
The lowest part of the spine is called the lumbar spine. This area has five vertebrae. However, sometimes people are born with a sixth vertebra in the lumbar region. The base of your spine (sacrum) is a fusion of many bones, and when one of them forms as a vertebra rather than part of the sacrum, it is called a transitional (or sixth) vertebra. This occurrence is not dangerous and does not appear to have any serious side effects.
The lumbar spine’s shape has what is called a lordotic curve. The lordotic shape is like a backwards “C”. If you think of the spine as having an “S”-like shape, the lumbar region would be the bottom of the “S”. The vertebrae in the lumbar spine area are the largest of the entire spine, so the lumbar spinal canal is larger than in the cervical or thoracic parts of the spine. Because of its size, the lumbar spine has more space for the nerves to move about.
Low back pain is a very common complaint for a simple reason. Since the lumbar spine is connected to your pelvis, this is where most of your weight bearing and body movement takes place. Typically, this is where people tend to place too much pressure, such as: lifting up a heavy box, twisting to move a heavy load,
or carrying a heavy object. Such repetitive injuries can lead to damage to the parts of the lumbar spine.
GLOSSARY OF TERMS
Annulus Fibrosis: tough fibrous ring around the disc.
Anterior: From the front of the body.
Anterior Column: the front 3/4 of the vertebral body and disc (as defined by a study by Denis). The column classification is used to determine the stability of the spine.
Autogenous Bone: bone originating from the same individual; i.e., a patient’s own bone.
Autograft Bone: bone transplanted from one part to another part of the body in the same individual.
Bone Morphogenic Protein (BMP): naturally occurring chemicals in the body- that play a major role in bone growth. BMP-like products are proteins that enhance mineralization and which can increase bone formation during fusion operation.
Bone Spurs: also called osteophytes.
Bulge of the disc: the form or position of the disc changes with some slight impingement into the spinal canal. Also called a prolapse or protrusion.
Cervical: Referring to the neck, the top seven vertebrae of the spine.
Corpectomy: Removal of the vertebral body, usually to remove pressure off of the spinal nerves.
Degeneration of the disc: chemical changes associated with aging causes discs to weaken, but without a herniation. These changes can be seen on MRI scans, and are usually asymptomatic.
Diagnostic Tests: include MRI, X-ray, CT scan, bone scan, discogram, myelogram.
Disc (also spelled Disk): the structure between the vertebral bodies.
Discectomy: removal of the disc.
Extrusion of The Disc: the gel-like nucleus pulposus breaks through the tire-like wall (annulus fibrosus) but remains within the disc.
Foraminotomy: opening of the foramen where the nerve exits.
Kyphosis - roundback (when viewed from the side). The thoracic spine is normally kyphotic.
Laminectomy: removal of the lamina.
Laminotomy: partial removal of the lamina.
Lordosis: swayback (when viewed from the side). The cervical and lumbar spines are normally lordotic.
Middle Column: the posterior portion of the vertebral body and disc (as defined by a study by Denis). The column classification is used to determine the stability of the spine.
Myelopathy: spinal cord dysfunction usually caused by compression. Signs include hyperreflexia (heightened reflexes), balance difficulties, dropping items and lack of coordination, and bowel and bladder dysfunction.
Natural History: what the patient’s outcome would be in given disease or condition without intervention (naturally).
Nucleus Pulposus: the soft inner core of the disc.
Neuroforamina: the tunnels where the nerve exists from the spinal canal to the arms and legs.
Osteophyte: bone spur.
Pars Interarticularis: a posterior bony structure between two adjacent facet joints in the lumbar spine. This structure is stressed and may fracture with extension and rotation of the lumbar spine.
Postlaminectomy Spondylolisthesis: a slipped vertebral body which occurs post-operatively, if the remaining bones are not strong enough to support the spine.
Posterior: from the back of the body.
Posterior Column: the facet joint, lamina, pars, spinous process, and adjoining ligaments. The column classification is used to determine the stability of the spine.
Posterior Longitudinal Ligament: ligament between the vertebral body and discs in front, and the spinal cord or nerve sac in back.
Prolapse of The Disc: the form or position of the disc changes with some slight impingement into the spinal canal. Also called a bulge or protrusion.
Protrusion of The Disc: the form or position of the disc changes with some slight impingement into the spinal canal. Also called a prolapse or bulge.
Pseudoarthrosis: lack or failure of fusion.
Radiculopathy: arm or leg pain being caused by nerve impingement or irritation.
Radicular: pain radiating down the arms or legs.
Scoliosis: curvature of the spine when viewed from the front or back. The curvature is usually associated with rotation of the vertebral bodies.
Sequestration or Sequestered Disc: the nucleus pulposus breaks through the annulus fibrosus and lies outside the disc in the spinal canal (HNP).
Stenosis: tightness and compression of the spinal cord, nerve roots, or dural sac.
Strut Graft:A long piece of bone or cage that is inserted into the space created by corpectomy to support (struts) the anterior column of the spine.
Spondylolisthesis: the slipping of one vertebra onto another.