The spine is an area of the body that we don’t think too much about until something goes wrong. We’re so used to being able to bend forward, arch backward, twist at our waist, and turn our head from side to side that we may forget that our back and neck are made up of an extremely complex network of bones, cartilage, muscles, ligaments, tendons, and nerves. In fact, the spinal canal houses the spinal cord, which, in conjunction with the brain, comprises the central nerve center of our body and allows us to experience everything from jumping for joy to physical pain.
In the event that some sort of injury or anatomical abnormality in the spine disrupts the cylindrical structure of the spinal canal, this long, hollow passageway for the spinal cord can actually become too narrow, which is referred to as canal stenosis (“stenosis” means “narrowing”). Canal stenosis can have a variety of different causes and can lead to many different types of symptoms, but the best way to understand how canal stenosis develops in your spine and affects your wellbeing is to have a clear picture of the spinal anatomy.
The Anatomy of Canal Stenosis
Canal stenosis usually involves several elements of the spinal anatomy, depending on the underlying cause of the spinal narrowing. Taking a look at each part of the spine and how it affects the other parts helps provide a clearer sense of how an injury or other type of condition in the back or neck can cause a chain reaction that eventually narrows the spinal canal.
Vertebrae – These are segments of bone that form the structure of the spinal column. They house and protect the spinal cord, and allow us to maintain an upright posture. Most people have 33 vertebrae in their spinal column, beginning at the base of the skull and culminating in the coccyx, or tailbone. The top two dozen or so vertebrae are made up of a large, solid segment of bone called the vertebral body that faces the front of the body, and a hollowed out, arched portion (shaped a bit like a wishbone) that faces the back of the body and forms the vertebral foramen.
Vertebral foramen – The term “foramen” refers to an opening in the body, and the vertebral foramen is the opening at the center of each vertebral arch. The foramina of the stacked vertebrae align to form the long spinal canal that houses the spinal cord.
Intervertebral foramen – In addition to the central vertebral foramen, each pair of vertebrae fits together to form two small, open canals on either side of the spinal column. These foramina function as passageways through which spinal nerve roots pass as they branch off the spinal cord to form the peripheral nerves that exist throughout the entire body.
Intervertebral discs – One cartilaginous disc lies in between and separates two vertebrae. This vertebra-disc-vertebra-disc assembly extends from the neck to the lower back. The 23 or 24 total discs in the spine play a ligamentous role by connecting the vertebrae, and also help absorb shock and lend flexibility to the spine.
Spinal column – The articulating vertebrae and intervertebral discs comprise the spinal column, which is the protective sheath that encases the spinal cord. Viewed from the side, the spinal column forms an S-shaped curve, made up of the cervical (neck), thoracic (middle back), lumbar (lower back), sacral (pelvic), and coccygeal (tailbone) regions.
Spinal canal – The spinal column itself does not touch the spinal cord. Instead, the cord is suspended in cerebrospinal fluid and covered by the meninges in the hollow space formed by the stacked vertebral arches. Blood vessels and spinal nerve roots are also present in the spinal canal.
Spinal nerve roots – There are 31 pairs of nerve roots that branch off the spinal cord; each pair consists of a ventral (motor) and a dorsal (sensory) root. These pairs join to form the spinal nerves that travel through the intervertebral foramina (passageways in between vertebrae) and separate into branches that innervate the entire body. While the roots are part of the central nervous system (CNS), once they join and form single spinal nerves, they become part of the peripheral nervous system (PNS).
Spinal cord – This is the long, thin rope of nervous tissue that, with the brain, comprises the central nervous system. Its length is between 43-45 centimeters and its thickness ranges from ¼ inch in the thoracic region to ½ inch in the cervical and lumbar regions. The spinal cord is the conduit between the brain and the peripheral nerves.
Clearly, all of these many components must work together to ensure the spine works normally, not just in terms of our everyday movements like walking and standing upright, but also in terms of how we perceive and respond to stimuli. Any of these important functions can be compromised if the spinal cord, spinal nerve roots, or the peripheral spinal nerves are subjected to stress, which is what can happen when canal stenosis occurs. Any type of anatomical abnormality, whether it involves a vertebra, intervertebral disc, or any of the many muscles, tendons, and ligaments that attach to the spinal column, can cause the space of the spinal canal to narrow, which puts our nerve structures in jeopardy.
Causes and Risk Factors of Canal Stenosis
It may seem like only a traumatic injury could cause a component of the spinal anatomy to become so damaged, misshapen, or displaced that it actually leads to a narrowing of the spinal canal. But because the spinal canal is so narrow and the structures it houses are so fragile, it actually doesn’t take much to cause stenosis and subsequent neural distress.
When exploring the causes of canal stenosis, it’s important to keep in mind that the spinal cavity does not just spontaneously narrow. There is always an underlying condition that leads to the stenosis, the nature of which your doctor will try to determine when formulating a canal stenosis diagnosis.
Below are a few of the possible conditions that have been known to cause canal stenosis:
Herniated disc – a degenerated intervertebral disc develops a tear in its tough, outer wall (annulus fibrosus) through which its inner gel-like material (nucleus pulposus) can seep into the spinal canal.
Bulging disc – a degenerated intervertebral disc balloons out to one side and into the spinal canal; the disc is still intact and the nucleus pulposus is still contained, but the disc’s outer wall can no longer maintain its structural integrity.
Spondylolisthesis – a vertebra, either due to degeneration, injury, or another condition, slips out of place in relation to adjacent vertebrae and protrudes anteriorly (toward the front) or posteriorly (toward the back).
Joint hypertrophy – the joints of the spine, called the facet joints, allow adjacent vertebrae to articulate. However, arthritis can cause these joints to become inflamed or abnormally enlarged, possibly causing them to invade the space of the spinal canal.
Bone spurs – arthritic facet joints lose cartilage over time and discs lose their height, which may lead to bone-on-bone contact between the vertebrae and the growth of bone spurs, or osteophytes, in the joints and around the edges of the vertebrae.
Ligament hypertrophy – a series of ligaments called the ligamenta flava help keep the vertebral column aligned, though over time these and other ligaments can harden due to the formation of calcium crystals and new bone deposits, making the ligaments become abnormally large.
Trauma – sudden trauma, such as an automobile accident or a sports injury, may cause the spinal canal to narrow, usually due to a fracture that has forced the displacement of a vertebra.
Spinal tumors – abnormal growths of soft tissue or bone can invade the spinal canal or displace vertebrae or intervertebral discs.
Paget’s disease – a chronic bone disorder that results in excessive formation of new bone that is porous and brittle, resulting in abnormally large vertebrae when the spine is affected.
Ankylosing spondylitis – a form of spinal arthritis that causes the facet joints to become inflamed and, in severe cases, causes the formation of so much new bone that the vertebrae are permanently fused together.
Congenital conditions – scoliosis and achondroplasia (dwarfism) are two inherited conditions that lead to abnormal spine growth and the possibility of canal stenosis.
After reading about some of the possible causes of canal stenosis, you may be wondering if there is any way for someone to avoid the condition. After all, diseases, congenital disorders, traumatic injuries, and many of the other causes are not things that can be predicted or avoided. In addition, causes that are primarily due to degeneration, such as herniated discs, bulging discs, and spinal osteoarthritis, are also difficult to avoid, since most spinal degeneration is simply a direct result of the natural aging process.
However, there are a variety of ways that individuals can keep their spines as healthy as possible as they grow older, which may mitigate spinal degeneration and possibly put off, if not prevent, the development of canal stenosis. Some of these efforts include:
Maintaining a healthy body weight
Quitting smoking and limiting alcohol consumption
Regularly taking part in low-impact exercises
Avoiding high-impact activities and contact sports
Trying to maintain proper posture at all times
Canal Stenosis - Symptoms
Canal stenosis is not inherently painful and does not always produce symptoms. It’s possible for someone to develop a degenerative condition like a herniated or bulging disc that protrudes into the spinal canal and causes this cavity to narrow, but if the disc material never comes into contact with a spinal nerve root or the spinal cord, it’s likely that the person will never even know they have the condition. When neural compression does come into play, however, discomfort can ensue, ranging from intermittent, mild pain to chronic, debilitating symptoms.
Symptoms of canal stenosis will obviously vary from person to person and will depend largely on the severity of the condition, at which level of the spine the canal has narrowed, and what underlying condition is behind the spinal narrowing. Two basic ways to categorize canal stenosis symptoms is to determine whether they’re being caused by compression of a spinal nerve root or the spinal cord. The former leads to radiculopathic symptoms and the latter leads to myelopathic symptoms:
Radiculopathy – may involve pain, tingling, cramping, numbness, and weakness that travel from the back or neck and into the extremities. Since nerve roots are the origin of the peripheral nerves that branch off to innervate the rest of the body, compression of a root tends to send distress signals along the entire path of the nerve, which is why symptoms may be felt as far away as the fingers and toes. Many forms of radiculopathy will be unilateral, or affecting only one side of the body. Radiculopathy is most common in the lumbar (lower) spine, since the weight-bearing responsibility of this region puts it at greater risk for abnormalities like stenosis, and symptoms will likely be felt in the left or right hip, buttock, leg, and/or foot.
Myelopathy – since this involves compression of the spinal cord itself, the symptoms may feel more dispersed than those of radiculopathy. Myelopathy often affects both sides of the body, and will feel more stationary in nature, as opposed to traveling symptoms that occur with nerve root compression. Spinal cord compression is most common in the cervical, or upper, spine. The spinal cord normally ends around the first or second lumbar vertebra, so spinal cord compression in the lumbar (lower) spine is less likely. Spinal cord compression in the neck may cause arm pain, a reduction in motor skills, or paralysis. It’s not uncommon for someone with cervical stenosis to have trouble tying a shoe, typing, or buttoning a shirt.
The nature of canal stenosis symptoms can sometimes make them hard to identify and diagnose. For instance, you wouldn’t intuitively know that pain or cramping in one leg is being caused by a nerve-related condition in your lower back. It’s extremely important to get a diagnosis from a medical professional if you think you may be experiencing discomfort that could be related to canal stenosis.
Regardless of what your ultimate diagnosis turns out to be, the best way you can help your doctor arrive at an accurate conclusion is to keep a thorough record of your symptoms. Note their severity, location, and nature, making sure to inform your doctor of any activities that exacerbate your discomfort.
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