The lumbar spine is made up of five vertebral bodies in the lower back. Nerves coming off the spinal cord travel though the spinal canal and exit the canal through small openings on the sides of the vertebrae called foramina (singular = foramen).
These nerves transmit sensations from the buttocks and lower extremities through the spinal cord to the brain and transmit motor signals from the brain to the lower extremities to produce movement of the legs, toes, and joints of the lower extremities.
Lumbar spinal stenosis is a condition whereby either the spinal canal (central stenosis) or one or more of the vertebral foramina (foraminal stenosis) becomes narrowed.
If the narrowing is substantial, it causes compression of the spinal cord or spinal nerves, which causes the painful symptoms of lumbar spinal stenosis, including low back pain, buttock pain, and leg pain and numbness that is made worse with walking and relieved by resting.
Lumbar Spinal Stenosis Symptoms
The typical symptom is increased pain in the legs with walking (pseudoclaudication), which can markedly diminish one’s activity level.
Patients with lumbar spinal stenosis are typically comfortable at rest but cannot walk far without developing leg pain. Pain relief is achieved, sometimes almost immediately, when they sit down again.
For most people, symptoms of lumbar stenosis will typically fluctuate, with some periods of more severe symptoms and some with fewer or none, but symptoms are not always progressive over time.
For each person, the severity and duration of lumbar stenosis symptoms is different and often dictates whether conservative (non-surgical) treatment or lumbar spinal stenosis surgery is more suitable.
The symptoms of lumbar stenosis generally develop slowly over time (most patients are over 50) and symptoms may come and go. Lumbar stenosis symptoms may include:
- Leg pain (sciatica)
- Leg pain with walking (claudication)
- Tingling, weakness or numbness that radiates from the lower back into the buttocks and legs.
What causes lumbar spinal stenosis?
The most common cause of lumbar spinal stenosis is degenerative arthritis and degenerative disc disease. As with other joints in the body, arthritis commonly occurs in the spine as part of the normal aging process and as a result of osteoarthritis.
This can lead to loss of the cartilage between the bones at the joints, formation of bone spurs (osteophytes), loss of the normal height of the discs between the vertebrae of the spine (degenerative disc disease, also known as spondylosis), and overgrowth (hypertrophy) of the ligamentous structures.
Further degeneration of the lumbar discs can lead to slippage of one vertebra on another, a process referred to as spondylolisthesis.
Each of these processes can reduce the normal space available for the nerves in the spinal canal and result in direct pressure on nerve tissues to cause the symptoms of lumbar spinal stenosis.
Lumbar spinal stenosis can also be caused by other conditions that decrease the space of the spinal canal or vertebral foramen. These can include
- tumor of the local structures or metastatic tumors (tumors that originated in another part of the body and spread to this location),
- various metabolic bone disorders that cause bone growth, such as Paget’s disease of bone.
These causes, however, are much less common than degenerative arthritis.
What are risk factors for lumbar spinal stenosis?
The major risk factor for lumbar spinal stenosis is aging because it is associated with degeneration of the spine.
Another, less common risk factor is osteoporosis as it can lead to compression fracture of the lumbar vertebrae that results in lumbar spinal stenosis.
Lumbar Spinal Stenosis Diagnosis
When a patient presents with the typical symptoms of lumbar spinal stenosis (leg pain, with or without back pain, which is aggravated by walking), a conclusive diagnosis is made using imaging studies from an MRI scan or a CT scan with myelogram (using an x-ray dye in the spinal sack fluid).
Physical examination alone does not yield a conclusive lumbar stenosis diagnosis.
There are three major types of stenosis and accurate identification is vital to stenosis treatment:
- Lateral stenosis. The most common type of spinal stenosis, lateral stenosis occurs when a nerve root that has left the spinal canal is compressed by either a bulging disc, herniated disc or bone protrusion beyond the foramen (a bony, hollow archway through which all spinal nerve roots run).
- Central stenosis. Occurring when the central canal in the lower back is choked, central stenosis may lead to compression of the cauda equina nerve roots (the bundle of roots that branch off at the bottom of the spinal cord like a horse’s tail).
- Foraminal stenosis. When a nerve root in the lower back is pressed on and trapped by a bone spur in the foramen, or the opening where the nerve root leaves the spinal canal.
What is the treatment for lumbar spinal stenosis?
In most situations, the treatment for lumbar spinal stenosis begins with conservative (nonoperative) treatments. This can include medications to reduce inflammation, even short courses of oral cortisone medication, and pain medications.
There are also several medications directed specifically at nerve pain that are helpful in lumbar spinal stenosis, including gabapentin (Neurontin) and pregabalin (Lyrica).
Physical therapy can help for many. Cortisone (steroid) injections in the lumbar spine, referred to as epidural injections, can also reduce the symptoms by decreasing inflammation and swelling around the nerve tissue.
These are sometimes repeated up to three times per year.
Surgery may be indicated for those who do not improve with the above treatments or if there is severe or progressive weakness or loss of bowel or bladder function (cauda equina syndrome).
Depending on the examination findings and imaging studies, there are various surgical procedures available to treat lumbar spinal stenosis, ranging from laminectomy to fusion procedures.
The main goal of surgery is to remove the structures that are compressing the nerves in the spinal canal or vertebral foramen.
This is referred to as lumbar decompression surgery (laminectomy, laminotomy, foraminotomy). In some patients, this can be performed alone, but in other patients, it must be combined with lumbar fusion.
If too much of the compressive structures need to be removed to free the nerve, the vertebrae may become unstable (spinal instability). This leaves the vertebrae with abnormal motion.
If this occurs, a spinal fusion can be performed to attach the vertebrae together and eliminate the motion at that level.
Sometimes this requires metallic hardware to be installed in the vertebrae to adequately support and fix the involved bone.
Surgery for lumbar spinal stenosis can be very successful in most patients in relieving the leg symptoms of ambulatory pain, sciatica, and numbness.
However, depending on the severity of the nerve compression and the length of time the nerve have been compressed, there may be some permanent damage that is not relieved with surgery.
The success for back pain relief is less reliable with surgery than the relief of leg symptoms.
More recently, surgical procedures that are somewhat less invasive than traditional lumbar decompression have become available.
Interspinous devices that have been used in certain patients for this purpose include X-Stop and Coflex devices.