Lumbar spinal stenosis (LSS) is a low back pathology that describes the narrowing of either the spinal canal or the neuroforamina the lower extremity nerves pass through. To better understand this pathology, we first need to discuss the basic anatomy and cover a couple definitions.
Stenosis: An abnormal narrowing of a passage in the body.
Foramen, Foramina, Neuroforamen: An opening or hole especially in bone. When “neuro” is put in front of the word, we are specifically describing a passageway that a nerve will travel through.
Our vertebral column is made up of 24 bones. In addition to providing a skeletal structure to our organs and muscles also houses our spinal cord. The spinal cord runs directly down the middle of our vertebral bones from the base of the skull all the way to the pelvis. It travels through the spinal canal. At each vertebral level the spinal cord will have nerve roots that branch off and provide nerve supply to the extremities. There are always two nerve roots per level and each supply their respective sides of the body. Picture the spinal cord as a tree trunk and each nerve root is a branch extending off the trunk. To exit the spinal canal, the nerve roots will pass through a neuroforamina (or a passageway) before they extend to the rest of the body.
As previously described, stenosis is a narrowing of a passageway in the body. In LSS we are referring to two specific areas that can become narrowed. The neuroforamina where the nerve roots exit the spine is one location and the spinal canal itself is the other. When the neuroforamina is obstructed, we typically present with single sided symptoms.
These are commonly due to disc herniations and often described in laymen’s terms as a “pinched nerve.” We discuss standard disc herniations in more detail here. Today we will be focusing on a narrowing of the spinal canal which may be more specifically termed “Central Spinal Canal Stenosis”.
There are numerous causes for the narrowing of these passageways, including severe disc herniations, chronic degenerative changes to the bone, traumas, or infections to name a few. In all of these examples, there is some change to either the soft tissue or bone that has led to the narrowing of the spinal canal. In an acute lumbar spinal stenosis, the patient may have sustained a trauma causing a severe lumbar disc herniation that can protrude into the spinal canal and impinge the spinal cord. Although acute traumatic cases occur, we see chronic cases of LSS far more frequently. Chronic cases are almost exclusively present in patients over the age of 50 and most prevalent in the 6th or 7th decades of life.
In the chronic LSS, the changes in your anatomy that may lead to stenosis are more likely to be degenerative changes of the spine such as bone spurs. In many cases “spinal degeneration” is a normal part of aging, often compared to wrinkles of the skin. Often, these “wrinkles” will have no symptomatic significance, but in more severe cases these bony growths can actually begin to narrow or cause “stenosis” where the nerves pass through. When these passages become too narrow, the nerves that pass through them can be impacted. This may lead to numbness, tingling, radiating pain or in more serious cases loss of muscular strength.