Spinal stenosis it a narrowing of the spinal nerve routes in one or both of two different canals or anatomic tunnels through which the spinal nerves travel. The spinal cord is a solid structure of nerves extending from its exit at the base of the skull to approximately the level of the first lumbar vertebral bone and continuing as separate but parallel nerve roots down to the second sacral level. Throughout its route the spinal cord travels through the central canal which is one anatomic tunnel that can have stenosis or narrowing. The second area of narrowing or stenosis is the neuroforaminal openings occurring to the left and the right at each vertebral level; a separate nerve root travels through the left and right tunnels at each level of the vertebral body on their way to the body. They carry impulses from the brain to muscles and sensory impulses to the brain from a specific area of the body called a dermatome.
Causes of Lumbar Spinal Stenosis
Normally these anatomic tunnels are open and there is no compression of the nerves inside but degeneration and collapse of the intervertebral disc height, herniation of the discs, or overgrowth of the anchoring ligaments can intrude into the anatomic tunnels and cause nerve compression. Spinal stenosis can also occur from birth but these cases are not usually symptomatic until other factors such as above start to happen.
Symptoms of Lumbar Spinal Stenosis
The symptoms of spinal stenosis may vary largely in degree than difference depending on the area of the stenosis. If the central canal is stenosed, then symptoms are classically described as neurogenic claudication which is walking or standing provoked back pain, leg pain and/or leg fatigue or weakness that promptly goes away when sitting or lying down or leaning forward as on a grocery cart when walking or standing. If the neuroforaminal canal is stenosed, then similar symptoms to central stenosis are encountered but only to the side that is narrowed; there may be more prominent leg pain present in addition to the leg fatigue. If both neuroforaminal canals are stenosed, it is difficult to tell the difference between central or neuroforaminal stenosis narrowing as the cause of the symptoms.
Diagnosis of Lumbar Spinal Stenosis
Because spinal stenosis is toward the end of the spinal degenerative cascade, it is usually seen in older age groups where degenerative processes have been ongoing for several years. The history and physical examination can result in a high likelihood of spinal stenosis but imaging studies are confirmatory. The spinal tunnels need to be imaging in cross section so CT scans or MRI scans will be needed by the providers if not already done. Contrast administration, in the case of CT, via spinal puncture may be needed to thoroughly evaluate the anatomy if MRI cannot be done.
Treatment of Lumbar Spinal Stenosis
The two pain generators in spinal stenosis are directly from the compression of the nerves that are trapped in the anatomic tunnels that are narrowed or stenosed. Because the nerves move within the tunnels as the body change position, the nerves can become irritated and inflamed. The treatment of this part of the pain is with anti-inflammatory medication taken orally and, if that fails, then by injected steroids into the narrowed tunnels with a needle placed under x-ray (fluoroscopy) guidance. These injections are intra-laminar epidural steroid injection (ILESI) or transforaminal epidural steroid injection (TFESI). The second pain generator involved is from the compression of the nerve in the segment inside the anatomic narrowed tunnel which leads to nerve dysfunction such that the sensory component t of the nerve will abnormally carry pain impulse to the central nervous system and cause weakness/fatigue in the muscles that the nerve controls. When the body position changes to upright as in standing or walking the curvature of the lumbar spine will change in a way that the central canal and the neuroforaminal canal will narrow further; this is why the upright position will often be the circumstance where the spinal stenosis symptoms are first felt. Treatment of this compression pain generator are typically first approached with medications that can calm internal nerve pain impulses by depressing impulse development in the affected nerve: examples of these medications include gabapentin, pregabalin, amitriptyline, and nortriptyline. There are two complex and minimally invasive procedures that can improve the stenosed area of the central canal and which may improve the size of the neuroforaminal canal indirectly. MILD (minimally invasive lumbar decompression) procedure done as an outpatient is removal of overgrown ligament in the central canal via needles introduced in the back after local anesthesia is injected and sedation provided by an anesthetist. Vertiflex procedure done as an outpatient is placement of a mechanical spacer that holds the central canal open when the body assumes the upright position which prevents further narrowing of the anatomic canals. The device is placed via a needle introduced in the back after local anesthesia and anesthetic sedation is performed.