Definition: Stenosis means narrowing of the spinal canal causing compression of the nerves or spinal cord. In the lumbar spine it is the nerves that go to the legs that are compressed.
Signs and symptoms: Spinal stenosis causes what is called neurogenic claudication. The person experiences pain and weakness in the legs when they walk. As the stenosis gets worse the distance a person can walk before they experience their symptoms becomes progressively less. Eventually people can walk less than a block without having to stop and sit down. Bending forward often relieves their pain. Therefore a person commonly stands or walks in a partly flexed forward position often with their knees partly flexed as well. Many people resort to using a cain or a walker. Walking on a hard surface such as in a mall often makes their symptoms worse. Leaning on a shopping cart often improves their symptoms and allows them to walk further. Standing in one position, such as in line at a checkout will also make their symptoms worse. Some people also develop numbness or tingling in their legs. Lying down or bending backwards also can make their symptoms worse. People can have difficulty sleeping in bed and resort to sleeping in their recliner in a partial sitting position. In severe cases people can develop problems with bladder control. Some people also experience back pain but many do not.
Causes: Spinal stenosis often results from a combination of factors associated with aging. Discs are structures that are located between each vertebrae in the front of the spine. The outer portion of the disc is called the annulus and is composed of layers of tissue that surround a central nucleus which is soft and provides cushioning for the spine. As the spine ages the layers of fibrous tissue weaken and expand resulting in bulging of the disc into the front of the spinal canal which results in narrowing the space for the nerves. The back of the spine has bones called lamina and joints called facet or apophyseal joints. The joints frequently develop osteoarthritis which results in enlargement due to thickening of the bone and the development of osteophytes or bone spurs. This bony enlargement also results in narrowing of the spinal canal from the sides and compression of the nerves. The third change which occurs with aging and contributes to the development of spinal stenosis is the thickening of the ligaments between the lamina at the back of the spinal canal. The degree of narrowing of the spinal canal is graded as mild, moderate and severe based on the measurement of the diameter of the spinal canal. Most people begin to develop symptoms once the narrowing becomes moderate and the symptoms become worse at the narrowing becomes more severe. Spinal stenosis usually occurs in people in people sixty years old or older due to the progressive degenerative changes in the spine that occur with aging. It is uncommon in younger people. diagram: 1 bulging disc, 2 enlarged facet joints, 3 thickened ligaments
Natural history: In most cases the symptoms come on slowly and progressively get worse over months or years. The symptoms can fluctuate and can disappear for a variable period of time before returning. In some cases they can resolve without returning.
Testing: The history is the most important assessment in making the diagnosis. The physical examination can be normal if their is no nerve damage. However if the nerves are compressed enough the examination can show signs of muscle weakness, sensory changes and loss of reflexes in the legs. The two diagnostic imaging tests that are commonly used to diagnose lumbar spinal stenosis are computed tomography (CT) scans and magnetic resonance imaging (MRI) scans. Both will show the narrowing of the spinal canal. MRI is better as it shows the nerves more clearly and the degree of stenosis is easier to determine on MRI than on CT scans. Upright MRI machines can take pictures of the spine with people in different positions such as lying, sitting, standing and bending which can give more information about the severity of the stenosis and show if their is any instability that might require a fusion-type of operation. Electromyography (EMG) and nerve conduction studies (NCS) can help determine which nerve is causing the symptoms if the nerves are being damaged. However EMG studies can be normal if there is no damage.
Treatment: The symptoms can be improved with medication such as anti-inflammatory drugs such as ibuprofen or prescription medication. Muscle relaxants can be helpful but often cause side effects such as drowsiness. Spinal epidural injections of local anesthetic and steroid medication can improve symptoms, sometimes for several months. However since this is a structural problem, which medications do not change, the pain relieve with medication or injections is often temporary. Physiotherapy, traction, massage therapy and chiropractic treatment can often provide relief for variable periods of time. If the symptoms become severe enough and are not relieved with medication or non-surgical therapy then surgery can provide pain relief. The most common operation for lumbar spinal stenosis is called a decompressive laminectomy.
This involves the removal of bone and ligament from the back of the spine to make more room for the nerves that are being compressed. This decompression procedure often results in significant improvement in their symptoms. People can stand and walk without pain or weakness in their legs. They stand up straighter and appear taller. Other forms of treatment for spinal stenosis are available and are sometimes less invasive. Implanting a spacer between the spinous processes can stretch the ligaments and open the space in a manner similar to what occurs when the person bends forward. If people have back pain in addition to the leg pain and weakness it can be due to the arthritis in the facet joints or due to abnormal movement between the vertebrae which is referred to as instability. Decompression operations such as laminectomies can make instability worse or can lead to the development of instability and back pain. Therefore if back pain is a major symptom in someone with spinal stenosis then a fusion (link to fusion) is sometimes performed in addition to the decompression.
Results of surgery: Operations are most frequently performed for relief of pain in the legs. No operation has a 100% success rate. For decompressive laminectomies the success rate is reported to be 70 – 80% of cases. The operation often improves the back pain but may not relieve it completely. If people have suffered nerve damage they may continue to have numbness or weakness in their legs which can improve over several months following the surgery but sometimes never goes away completely. Failure to improve after surgery can be do to ongoing nerve compression from inadequate decompression, nerve damage from the nerve compression by the stenosis or as a result of the surgery, incorrect diagnosis (meaning that the spinal stenosis was not the cause of the symptoms in the first place) or due to the development of instability. Recurrence of symptoms can occur due to the development of stenosis at the same level or at a new level in the spine.
Possible complications of surgery: Surgery has a number of potential risks, most of which occur infrequently but must be considered when contemplating surgery. Infections occur in approximately 1 – 5 % (1-5 in 100) of operations and can usually be treated with antibiotics. Repeat surgery is sometimes necessary. Nerve root injury can occur and can result in numbness or loss of feeling in part of the leg or weakness in the muscle that the nerve controls. Tearing the membrane (dura) that surrounds the nerves causes leakage of spinal fluid which can be treated by suturing the dura or covering the whole with substance to stop the leak. This can result in the development of headaches that are worse when the person sits or stands and improves when they lie down. Bed rest for 24 – 48 hours often corrects the problem. Other more serious complications include pneumonia, bladder infections, blood clots in the legs that can travel to the lungs, heart attacks, hospital acquired infections, instability of the spine. Most of these complications are uncommon and potentially avoidable.