What is lumbar spinal stenosis?
Lumbar spinal stenosis is compression of nerve roots within the central lumbar canal that may clinically present as radiculopathy, pseudoclaudication, or cauda equina syndrome. Spinal stenosis results from narrowing of the normal oval spinal canal, which can assume a triangular appearance in the diseased state due to facet hyperostosis, ligamentum flavum hypertrophy, broad-based central disc protrusion, spondylosis, or any combination. The typical patient has symptoms of lower limb claudication (neurogenic) in the absence of peripheral vascular disease. Symptoms are exacerbated by back extension and relieved with flexion, thus creating the classic simian posture. Pain is typically worsened when walking downhill due to back extension causing more stenosis. Patients will often report relief from walking-induced bilateral posterior buttock and thigh pain when they lean forward on their shopping carts. Symptoms may be produced by extending the patient’s back for 30 seconds (spinal Phalen’s).
This type of pain presentation is commonly noted in the aging population (those over the age of 60) who develop degenerative changes in the spine. Nonetheless lumbar stenosis can be created by a large central disc herniation. A combination of factors, including disc bulging, facet capsular hypertrophy, ligamentum flavum hypertrophy, and osteophyte formation, can all contribute to narrowing of the central canal. Spondylolisthesis can also contribute to central canal narrowing. Due to this narrowing, the spinal nerve roots that make up the cauda equina can be compressed and ischemic. Any of the potential nerve roots traveling distally can be affected by this tight squeeze. Also, the increase in intrathecal pressure, decrease in arterial flow, and venous congestion can additionally affect these nerve structures. A flexed posture will traditionally open the canal, while standing erect or extending the spine will promote increased intrathecal pressure. Manifestation of neurologic symptoms is described as neurogenic claudication. Sitting and lying flat provides symptomatic relief. Upright postures tend to narrow the canal; standing and walking are uncomfortable. Pain can be nonspecific, depending on the predominant nerve root(s) affected. A wide-based gait is the most common examination finding, followed by absent ankle reflexes (noted in less than half of sufferers). Diagnosis is made based on clinical findings in conjunction with neuroimaging. Noncontrast MRI of CT myelogram of the lumbar spine is recommended, since the soft tissue elements (ligament, joint capsule, disc) causing stenosis can be visualized, as well as the bony factors. Area in the canal less than 76 mm 2 marks severe stenosis; less than 100 mm 2 for moderate stenosis. Because spinal stenosis is most often due to degenerative changes, symptoms often persist long term. About 20% to 30% of those with stenosis are asymptomatic. On the other hand, those with lumbar stenosis can present with progressive disability. Conservative care includes physical therapy, NSAIDs or analgesic administration, and epidural injections. Should conservative approaches fail, surgery can be considered.