- Cervical (neck)
Thoracic (upper back)
Lumbar (lower back)
The sacrum lies at the base of the spine and consists of 5 fused vertebrae. It connects your spine to your pelvis. The coccyx, also known as the tailbone, lies at the end of the sacrum and is a set of 4 fused bones. Between most of these bones are intervertebral discs (of which there are normally 23). These discs allow motion between the vertebral bones and absorb shock from gravity and activity.
Within each region of the spine, the vertebrae are numbered from top down. There are 7 cervical, 12 thoracic, 5 lumbar and 5 sacral vertebrae.
A typical vertebra can be divided into an anterior (front) and a posterior (back) portion. The anterior portion and the posterior portion are separated by the central or spinal canal, where the spinal cord is located. The anterior portion of the vertebral bone consists of the vertebral body. This is a block of bone that supports most of your body weight (approximately 70%). The vertebral bodies lie directly on top of each other and are separated by intervertebral disks.
The posterior portion of the vertebra consists of a posterior (or neural) arch made of bone that encloses the spinal canal. This arch is formed by bone called the lamina. The pedicles connect the lamina to the vertebral body. The facet joints are formed by the superior articular process and inferior articular process of two adjacent vertebrae. They support approximately 30% of your body weight. The facet joints and the intervertebral disk together allow motion between two vertebrae. The spinous process and transverse processes provide additional support and protection to the spinal structures.
C1, also known as the atlas, is the first vertebra and articulates with the skull through the occipital condyles. This is where 50% of neck flexion and extension occurs. C2, also known as the axis, articulates with C1, where 50% of neck rotation occurs. C1 and C2 have very unique structures. C3 through C7 is known as the subaxial cervical spine and has relatively uniform anatomy. Nevertheless, C3-C7 differ from thoracic and cervical vertebrae in structure. Their facet joints are very flat, allowing for rotation and flexion/extension. They also have transverse foramina rather than transverse processes. Within the foramina travels the vertebral artery, which arises from the subclavian arteries in the upper chest. The vertebral arteries merge at the top of the cervical spine to form the basilar artery at the base of the brain. These arteries provide approximately 20% of the blood flow to the brain.
The spinal cord emerges from the brain and enters the spine through a hole called the foramen magnum at the base of the skull. It passes through the central canal of the cervical spine and the thoracic spine, giving off a pair of nerve roots at each level. These nerves pass under the pedicles of each vertebra on their way to the arms, torso or legs. The opening through which the nerves pass is called the neuroforamen. Within the cervical spine, the nerve that passes under the pedicle at a certain level is named for the level below it. For example, the nerve passing under the left C6 pedicle is the left C7 nerve root. The nerve that passes under the right C7 pedicle is the right C8 nerve root. Note that there is no C8 vertebra. From T1 down to the sacrum, the nerve that passes under the pedicle at a certain level is named that level. For example, the nerve passing under the right T1 pedicle is the right T1 nerve. The spinal cord continues down the spinal canal and ends approximately at the level of L1. The tip of the spinal cord is called the conus medullaris. The remainder of the spinal canal, within the lumbar and sacral spine, contains individual nerves as they travel to their exiting levels. This collection of nerves is called the cauda equina.
The spinal cord and the nerves within the spinal canal are bathed in spinal fluid. This fluid provides mechanical and immunological protection for the spinal cord and nerves. It is contained within a thin, water-tight sac called the dura mater. This is a continuation of the same spinal fluid and sac that bathes and protects the brain.
Nerves that leave the spinal cord and spinal canal innervate muscles and skin throughout the body. Sensation, pain, temperature, pressure and vibration are all sensed through these nerves. Each nerve innervates, or supplies, a single distribution along the torso or extremity. However, each nerve may innervate or provide partial innervation to one or multiple muscles.
A number of conditions can affect the spinal column. These include fracture, infection, cancer, congenital (birth) abnormalities, abnormal curvature and degeneration.
Degeneration can be thought of as wear and tear changes. Conceptually it is similar to arthritis. It is very common and is due to a complex interplay between many factors. Age, activity level and genetics are believed to be the largest factors associated with degeneration but occupational, environmental, recreational and traumatic exposures also play a role. It is generally believed that degeneration begins at the level of the intervertebral disc, where many changes can occur with age (or the other factors mentioned above). These changes lead to a loss of disc height. This loss of disc height can lead disc herniations (also known as bulges or ruptured discs). Continued loss of disc height can lead to narrowing of the neuroforamina or spinal canal. If these disc changes place pressure on the spinal cord or nerves, symptoms, including pain, numbness, weakness or other neurologic abnormalities in the extremities or torso can develop. As this degeneration proceeds, the disc can lose more height. When this occurs increased stress is placed on other structures, such as the facet joints. This increased stress can lead to degeneration in the facet joints, similar to that in the knee or hip. As the process continues, the affected vertebra can begin to shift. If the vertebra moves forward or backward, this is called spondylolisthesis. If the vertebra rotates or moves in a more complex manner, this can result in scoliosis. Movement of this kind does not always occur, however. Continued facet joint arthritis leads to bone spurs and enlargement of the facet joint. This can further narrow the spinal canal and/or the neuroforamina. Narrowing of this kind is called stenosis.
Disc herniations cause symptoms when they pinch or compress nearby nerves. Commonly referred to as sciatica, disc herniations classically cause shooting pain that runs down the leg into the foot, following the distribution of the affected nerve(s). Other symptoms may include numbness or tingling or muscle weakness. Disc herniations are very common but most do not cause symptoms. In fact, up to 40% of the population has disc herniations but may not experience symptoms. Disc herniations that do cause pain or other symptoms most commonly resolve within 3 months on their own.
For patient whose symptoms do not resolve, procedure can be performed where the affected nerves can be relieved of this compression. This surgical procedure is called a microdiscectomy. In this procedure, the herniated portion of the disc is removed through a small incision in your back. This is typically a day surgery, where patients can go home the same day.
As degeneration progresses, the vertebra can shift and cause narrowing of the spinal canal and the neuroforamina leading to spinal and neuroforaminal stenosis. This degeneration and change in the position of the vertebra can also cause back pain, which can involve the buttocks, hips and thighs.
Typically treatment begins with conservative measures, which include activity modification, pain medication, physical therapy and spinal injections.
For patients whose symptoms persists despite conservative managment, spine surgery is an option that can provide relief. Specific surgical details depend on the exact nature of the degeneration but typically include a decompression and fusion to relieve the stenosis as well as stabilize the spine.
Narrowing of the spinal canal can cause symptoms called neurogenic claudication. Claudication is discomfort or impairment in walking. There are two general kinds of claudication: Neurogenic (nerve related) or vascular (blood supply related). Blood supply issues usually arise from blocked arteries and can be addressed with a variety of vascular procedures performed by vascular specialists.
Neurogenic claudication results when the nerves in the lumbar spine are pinched by narrowing of the spinal canal. This is usually due to degeneration and/or disc herniations. This reduces blood flow and nutrients to the nerves, leading the nerves to function improperly. The symptoms include fatigue and/or cramping in the buttocks, calves and/or thighs with walking or standing for a period of time. This is typically reproducible with a specific length of activity. Often patients report the need to sit down to relieve their discomfort. The ability to tolerate activity is increased classically with flexion of the back (such as in walking uphill, cycling or pushing a shopping cart) as this increases the area of the spinal canal slightly.
Typically treatment begins with conservative measures, which include activity modification, pain medication, physical therapy and spinal injections. For those patients in whom these symptoms are significantly impairing their ability to function, spine surgery is an option. A decompression can be performed to relieve the stenosis and improve the claudications symptoms.
Low back pain
One of the most common complaints for patients seeking medical care is low back pain. In fact, 60-80% of people will have low back pain at some point in their lives. The vast majority of low back pain resolves within 3 months without the need for specific treatment. Unfortunately, there is a great deal we do not understand about low back pain. In up to 80% of patients with low back pain, a specific reason for their pain cannot be specifically identified. This “non-specific” low back pain is best treated with conservative measures such as anti-inflammatory medication, physical therapy and sometimes spinal injections. Research has shown that surgery for non-specific back pain does not reliably improve symptoms. For this reason, surgery for this common type of back pain is not recommended. At this time, more research is needed to identify the sources for back pain and the best surgical and non-surgical treatments.