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Spinal stenosis is a medical condition in which the spinal canal narrows and compresses the spinal cord and nerves. This is usually due to the natural process of spinal degeneration that occurs with aging. It can also sometimes be caused by spinal disc herniation, osteoporosis or a tumour.
Spinal stenosis may affect the cervical, thoracic or lumbar spine. In some cases, it may be present in all three places in the same patient. Lumbar spinal stenosis results in low back pain as well as pain or abnormal sensations in the legs, thighs, feet or buttocks, or loss of bladder and bowel control.
Spinal stenosis began to be recognized as an impairing condition in the 1960s and 1970s. Porter et al. discovered that individuals who experience back pain and other symptoms are likely to have smaller spinal canals than those who are asymptomatic. [1] Rothman reported that a normal sized lumbar canal is rarely encountered in persons with either disc disease or those requiring a de-roofing (laminectomy) procedure. [2] The natural evolution of disc disease and degeneration lead to stiffening of the intervertebral joint. This leads to osteophyte formation -a bony overgrowth about the joint. This process is called spondylosis, and is part of the normal aging of the spine. This has been seen in studies of normal and diseased spines. Degenerative changes begin to occur without symptoms as early as 25-30 years. It is not uncommon for people to experience at least one severe case of low back pain by the age of 35 years. This can be expected to improve and become less prevalent as the individual develops osteophyte formation around the discs. [3]
A certain minority of patients will go on to develop spinal stenosis by the age of 60 years. [4] Plain x-rays of the lumbar or cervical spine may or may not show spinal stenosis. The definitive diagnosis is established by either CT (computerized tomography) or MRI scanning. Identifying the presence of a narrowed canal makes the diagnosis of spinal stenosis. [5] [6] [7] [8] However, the diagnosis is based on clinical findings. Some patients can have a narrowed canal without symptoms, and do not require therapy. Stenosis can occur as either central stenosis – the narrowing of the entire canal, or foraminal stenosis – the narrowing of the foramen through which the nerve root exits the spinal canal. Severe narrowing of the lateral portion of the canal is called “lateral recess stenosis”. The ligamentum flavum (yellow ligament), an important structural component intimately adjacent to the posterior portion of the dural sac (nerve sac) can become thickened and cause stenosis. The articular facets, also in the posterior portion of the bony spine can become thickened and enlarged causing stenosis. These changes are often called “trophic changes” or “facet trophism” in radiology reports. As the canal becomes smaller and resembles a triangular shape, it is called a “trefoil” canal.
The normal lumbar central canal has a midsagittal diameter (front to back) greater than 13 mm., with an area of 1.45 square cm. Relative stenosis is said to exist when the anterior-posterior canal diameter between 10 and 13 mm. Absolute stenosis of the lumbar canal exists anatomically when the anterior-posterior measurement is 10 mm. or less. [9] [10] [11]
The first symptoms of stenosis are bouts of low back or neck pain. After a few months or years, this may progress to pain that is described as claudicant pain or claudication. This is a sensation of not getting enough blood to the arms or legs. It occurs more frequently in the legs. The pain may also be radicular in nature, following the classic neurologic pathways. This occurs as the spinal nerves or spinal cord becomes increasing trapped in a smaller space within the canal. It can be difficult to determine whether pain in the elderly is caused by lack of blood supply or stenosis. Modern testing can usually differentiate between them. Sometimes, patients will have both vascular disease in the legs and spinal stenosis. [12] [13] [14] [15]
In 1977, Dyck and Boyd [16] reported on the bicycle test of van Gelderen. The test has been intermittently reported in various places since then. It is a simple procedure in which the patient is placed upon a stationary bicycle, and asked to pedal. If the symptoms are caused by peripheral vascular disease, the patient will experience claudication by pedaling the bicycle in any position. If the symptoms are caused by lumbar stenosis, they will be reproduced only by having the patient lean forward while bicycling. Despite the fact that diagnostic progress has been made with newer technical advances, the bicycle test remains a cheap and easy way to distinguish between claudication caused by vascular disease and spinal stenosis. Dyck and Boyd wrote in their 1977 article: The authors describe a simple clinical adjunct to the routine neurological examination of patients with intermittent cauda equina compression syndrome. The “bicycle test” helps exclude intermittent claudication due to vascular insufficiency and frequently confirms the relationship of posture to radicular pain.
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