The narrow lumbar canal is called a narrowing of the vertebral canal, where the spinal cord is located, in the lumbar area, that is, in the lower back. In almost all cases, it is osteoarthritis that is at the origin of this pathology.
1. Definition of narrow lumbar canal
As the name suggests, a narrow lumbar canal (also known as lumbar stenosis) is a narrowing of the vertebral canal in the lumbar region. Remember that the vertebral canal is the space in which the spinal cord is located, from the first cervicals to the lumbar vertebrae. In order to understand this narrowing, it is necessary to go back to some notions of anatomy. Each of the vertebrae that make up the spine is separated from the vertebrae above and below by an intervertebral disc. The function of this gelatinous disc is to absorb the shocks and pressure to which the vertebrae are subjected, as well as to allow their mobility. As we age, the intervertebral discs naturally lose their effectiveness, so the vertebrae tend to come into contact with each other. The resulting friction is the cause of spinal osteoarthritis.
2. Causes of narrow lumbar canal
Osteoarthritis is the primary cause of a narrow lumbar canal. Indeed, it causes bone growths (osteophytes), which will develop and gradually narrow the vertebral canal. Lumbar osteoarthritis can also appear from the joints between the vertebrae, with the same risks of compression of the spinal cord and the nerve roots that emerge from the vertebral canal at this point (and which can be responsible for famous sciatica). Two other causes can also explain this narrowing: the thickening of the ligaments connecting the vertebrae between them, and the protrusion of the intervertebral disc (according to the same principle as a herniated disc). Note that the diameter of the vertebral canal varies from one individual to another. If the average size of the diameter is 16 mm (measured on the scanner), some people have a canal of only 13 mm, the size of which is considered narrow and therefore more at risk.
3. Symptoms of narrow lumbar canal
The symptoms of a narrow lumbar canal are caused by the compression of the nerves it creates. The nerves in question are those that manage the sensitivity and control of the lower limbs, and the damage may affect only one side of the body or both. Thus, depending on the extent of the nerve compression, one will find symptoms such as
persistent low back pain (in the lower back) ;
- sciatica-type pain, along the path of the sciatic nerve: in the buttock and the back of the thigh, with the possibility of pain reaching the foot;
- cruralgia-type pain, along the path of the crural nerve (formerly called femoral nerve): in the front of the thigh;
- motor disorders affecting the legs and sometimes the feet, which make walking difficult or even impossible. In this case, the lower limbs are unable to support the body due to a poor return of nerve information (this is called neurogenic claudication, according to the Mediterranean Back Institute);
- sensory disorders with sensations of pins and needles in the legs (paresthesias), numbness, or even loss of sensitivity;
- depending on the nerves affected, urogenital neurological disorders can sometimes be observed, including uncontrolled loss of urine, or anal incontinence (one can no longer contract the sphincters). This is known as cauda equina syndrome.
The symptoms of a narrow lumbar canal will inexorably increase over time. This evolution takes place over a few weeks, a few months, or even several years underlines the Paris Back Institute.
4. Diagnosis of narrow lumbar canal
An x-ray is usually required from the front and side to assess the condition of the lumbar vertebrae and their joints. This X-ray is prescribed in cases of persistent pain that cannot be relieved by standard medical treatment. Among other things, it allows us to eliminate other causes that could explain the pain. Additional examinations may be necessary, especially before scheduling an operation. These will include :
- a CT scan, which allows to locate precisely the osteoarthritic deformities and determine their size;
- an MRI (Magnetic Resonance Imaging), also to observe bone deformations, but also the damage to the intervertebral discs;
- a radiculography, which combines an X-ray and a scanner of the dural sac (the envelope of the spinal cord - that's why it's called "epidural", i.e. through the dural sac) in order to localize the zone in which the nerve compression is exercised;
- dynamic X-rays (performed leaning forward or bent backward) to evaluate the stability of the lumbar vertebrae;
- an electromyogram to test the function of the nerves and to evaluate the importance of the compression;
- bone densitometry to assess bone strength.
5. Treatments and physical therapy exercises for narrow lumbar canal
The initial treatment for the narrow lumbar canal is based on analgesics, which relieve pain, and muscle relaxants, which reduce muscle contractures. If the pain is severe, anti-inflammatory drugs (against pain and inflammation) may also be prescribed. In a second step, a rheumatologist may also perform infiltrations, i.e. injections directly on the nerve to be relieved. Up to three infiltrations can be performed, but if not enough relief is obtained, the next step is taken. Indeed, the treatment of narrow lumbar canal can also be surgical. An operation can relieve the pain and "free" the nerves, but it is not always possible. It is proposed in the most severe cases, when the neurological symptoms are too important (especially when they prevent walking, and even more so when there is a loss of sphincter control), or if they are accompanied by particularly intense pain that disrupts daily life.
The intervention can therefore also be proposed without going through the infiltrations. It is a decompression surgery, and in most cases a laminectomy, which consists in enlarging the spinal canal to decompress the spinal cord. However, it is contraindicated in cases of osteoporosis, as there is too high a risk of fracture. In case of lumbar instability, an arthrodesis (which consists of blocking several vertebrae together with metal rods and screws) must also be performed; it is also aimed at relieving pain. A final surgical option is an interspinous wedge. This involves placing a wedge between the vertebrae to relieve pressure on the nerves. If the conditions are met, in order to obtain good results and promote a good recovery, it is necessary to operate rather quickly. Indeed, waiting too long risks irreversible damage to the nerves, especially in the case of cauda equina syndrome. Following surgery, and in particular, in the case of arthrodesis, it is necessary to move as normally as possible from the day after surgery. Physiotherapy is useful to help with this, and will usually be prescribed for about a month. Normal physical activities and even lifting can be resumed after three months.
One study also concluded that a standard physical therapy program (2 sessions of 45 minutes per week for 6 weeks) had the same effect as surgery to improve the deficits caused by a narrow lumbar canal. And this, without side effects or risks of complication (source: "Surgery versus nonsurgical treatment of lumbar spinal stenosis: a randomized trial". Ann Intern Med. 2015 Apr 7). In fact, the work consists of a warm-up on a rehabilitation bike, a mobilization of the spine to decompress the lumbar vertebrae, and an individualized learning of muscle-strengthening exercises (dorsal and abdominal muscles that ensure spinal stability) and stretching to be performed at home.
6. Prevention of narrow lumbar canal
Prior to the onset of arthrosic problems or in their early stages, it can be interesting to consult an osteopath, who will be able to restore joint stability in the lumbar region. By avoiding vertebral blockages and their recurrences, osteoarthritis is less likely to develop, which reduces the risk of a narrow lumbar canal. More traditionally, physical therapy or any other approach that limits the development of osteoarthritis is a preventive technique.
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