1. What is it?

Lumbar canal stenosis, a narrowing of the vertebral canal in the lower spine, is a condition that is fairly frequent, especially in older people. Patients who have this condition complain of pain low down in the back and radiating into one or both legs. A typical symptom is that the pain manifests after some time of walking or standing; the pain in the back and in the legs gets worse, the legs feel numb and cannot be controlled. In order to lessen the pain, patients must sit down or lean forward or squat on their heels. Lying on the side, or with the legs drawn up, also tends to help. Simply remaining still but standing up after walking does not help as the symptoms appear even after long periods standing. While the normal walking posture is upright, the pain causes patients to walk slightly bent over, as in this position the symptoms are easier to bear. People with this complaint look forward less and less to going out for their daily errands or social occasions, so that they can ultimately become isolated from society. It is a remarkable fact that people suffering from lumbar canal stenosis can happily ride a bicycle without experiencing any leg or back pain worth mentioning. In order to get a good understanding of this condition it is important to know a little about the anatomy of the spine.

2. Cause

The cause of the symptoms is a narrowing, or stenosis, of the vertebral canal in the lower spine. Owing to the load it supports throughout the years, in older people the spine tends to show some wear and tear; this is a normal sign of aging that occurs in everyone, but the extent to which this happens is different from person to person. This type of wear and tear is called arthritis and is also common in the hip or knee joints. As a reaction to the arthritis the vertebral bones grow, becoming much thicker, especially at the joints, causing the vertebral canal to narrow. The yellow ligament, the strongest in the spine, running all along its length, also thickens, so that there is even less room left over in the narrowed vertebral canal for the cauda equina, a group of nerves resembling the tail of a horse, and the nerve roots. Whatever room there ultimately remains available is further limited by the degree of wear and tear and the width of the canal, which can both differ from one person to the next (Illustration 1).

The width of the vertebral canal is already different at birth, i.e. between one baby and the next. Those who were already born with a narrow canal will be more likely to suffer from this condition as a result of the wear and tear process as the reserve space will get used up more quickly. In patients whose canal is very narrow from birth, the condition can already manifest at a relatively young age.

Schematic drawing of a section through a lumbar vertebra

Illustration 1: Schematic drawing of a section through a lumbar vertebra. In order to show the spatial relationships more clearly, the section is made a little higher, through the dural sac, with the cauda inside, and shows the lining provided by the yellow ligament.

  • A: Normal "thin" vertebra. The vertebral canal is wide and triangular in section, the dural sac is of normal width, as are the nerve roots next to it; the yellow ligament lining is thin.
  • B: Arthritic vertebra. The excessive bone growth causes the contours of the vertebra to become rough and irregular, and the canal narrows to adopt a sort of T-shape. The dural sac is compressed sideways, as are the nerve roots, which also lack space, as in addition the yellow ligament lining thickens significantly, filling up a great deal of the canal.

Worsening stenosis symptoms are the result of a postural narrowing of the vertebral canal. When walking or simply standing up the position of the spine normally creates a "hollow back" (lordosis). This narrows the vertebral canal down, resulting after some time in congestion that causes compression of the nerve roots. When we bend forward or sit down, the lumbar spine returns from the hollow position to a straight or even slightly arched position. In these circumstances the vertebral canal is widest and the congestion disappears. There is once again more room for the nerve roots, and the pain eases. At the beginning, the stenosis often affects only L4/5 (the 4th and 5th lumbar vertebrae), because the canal is normally at its narrowest at this location, but with extensive stenosis other areas can also be affected (L3/4, L2/3 and even L1/2). The wear and tear process can also affect one or more intervertebral discs, which will then protrude, which in turn will naturally worsen the space problem. This space limitation will primarily occur when the wear and tear of the intervertebral discs develops into actual herniation; the radiating pain into the legs then behaves similarly as with a herniated disc, and becomes more acute with coughing or sneezing (see chapter on this subject).

3. Diagnosis

To determine with certainty whether the problem is a narrowing of the vertebral canal, transversal slices of the lumbar vertebrae are taken with a CT scan or an MRI, which will show significantly thickened vertebral bone at the expense of the room in the canal. Normally, the vertebral canal seen in a cross-section is triangular in shape, but with stenosis it adopts a sort of T-shape or even a narrow, flat shape. CT scans do not show the dural sac and its content (the cauda) as such, yet it is clear that there is little room left inside the narrowed canal (Illustration 2). CT scans are primarily useful for creating an image of the bone itself.

Cross-section through a lumbar vertebra

Illustration 2 : (left) Cross-section through a lumbar vertebra.

  • A: CT scan of a normal lumbar vertebra (at the intervertebral disc). The image shows the yellow ligament, the dural sac and its content and the nerve roots.
  • B: CT scan of a lumbar vertebra with canal stenosis. The vertebral canal has narrowed to a T-shaped cross-section; little can be seen of the yellow ligament, dural sac and nerve roots due to the contrast with the dominant bone image (in the same way as during the daytime the stars are not visible because the sun outshines them).
  • C: CT radiculography through the same vertebra with canal stenosis: through the addition of contrast medium into the dural sac, it becomes visible within the narrowed vertebral canal.
  • D: MRI through the same vertebra with canal stenosis: the image of the bone is no longer so dominant, while the surrounding muscles are more visible.
Lateral MRI of a lumbar canal stenosis

Illustration 3: (right): Lateral MRI of a lumbar canal stenosis; it shows the vertebral canal seen from the left with narrowed areas caused among other things by protrusion of the intervertebral discs, primarily L4/5, but also L3/4 and L2/3. To render the dural sac and its content properly visible it is necessary to introduce contrast medium, usually by means of an injection in the back, and then to carry out a CT scan called a CT radiculography. The diagnosis can also be made by means of an MRI that will show both the thickened bone and the vertebral canal and its content. With an MRI it is also possible to take longitudinal "slices" (images) of the body (i.e. from top to bottom) which will show the degree of narrowing in different areas as well as the wear on the intervertebral discs. A diagnosis of lumbar canal stenosis as the cause of the symptoms is necessary in order to rule out other conditions that manifest with similar symptoms, as different conditions will naturally require a different type of treatment. The first such other condition is intermittent claudication, the so-called "window-shopper's disease": Because of a narrowing of the blood vessels in the legs, the patient experiences leg pain after walking for some time, forcing him or her to stop, for example in front of a shop window, until the pain subsides. Furthermore, arthritis (wear and tear) of the hip joint can also cause pain in the thighs that can resemble that caused by lumbar canal stenosis.

4. After the operation

During the first few hours following surgery, patients must remain lying on their back so that any small bleeding blood vessels in the area affected by the operation can be closed by the pressure exercised by the patient's own body weight. The blood in the area affected by the operation is sometimes also drawn off by means of a drain. A catheter placed in the patient's bladder avoids the need to change position for urination purposes. The post-operative pain is caused primarily by the surgical manipulation of the bones, for which a painkiller is administered; it subsides quickly over the next few days. Most of the time it takes until then for the patient to notice that the old pain from before the operation has disappeared. Because older people have a significant tendency to develop thrombosis in the legs, especially after an operation, current practice is to get patients back on their feet as soon as possible in order to stimulate the circulation. Until they are fully mobile again they are also given medication to prevent thrombosis. Patients are also issued with anti-thrombosis stockings that must be worn at all times, including after the hospital stay, until their normal mobility prior to the operation is regained. With the aid of physiotherapy, if applicable, patients are mobile enough and ready to go home again one week later.

5. Risks involved in the surgery

Technically speaking, the operation does not involve much in the way of risk. On the other hand, if several areas need to be operated on at the same time, the surgery will be longer and there will be more loss of blood. Because most people with lumbar stenosis are older, the anaesthesia risk is greater (as concerns heart and lung complications). Recent development in the area of instruments means that operations can now be carried out in a maximum of one hour, thus only rarely requiring blood transfusions. It is however necessary to discontinue the use of anticoagulants and aspirin (10 days before surgery), if applicable with the approval of the patient's internist. To prevent thrombosis, our clinic administers a controllable anticoagulant either throughout or as from the day before the surgery; this medication would appear not to increase blood loss during the operation. In some clinics, circulation in the legs is stimulated by means of special elastic stockings or with stockings that are rhythmically inflated by a machine in order to prevent thrombosis. Thus the risks involved in the operation for older patients are primarily connected with their age and their general state of health, like heart and lung conditions which can make lying on one's front difficult to bear. With the latest developments in anaesthesia there is no longer an age limit for surgery, and, as a rule, the patient's health condition can be sufficiently managed by taking the required measures before and during surgery. As with hernia operations, here too the specific surgery related risks are an increase in deficiency or dysfunction symptoms (paralysis, loss of sensation) due to having to manipulate nerve roots that have been compressed for quite some time. When freeing a strongly pinched dural sac, a small tear can occur, leading to liquor leakage, which is remedied by means of flat bed rest for 3 to 5 days. Other rarely occurring risks are post-operative bleeding in the area affected by the surgery, and infection of the wound