Lumbar Spinal Stenosis

Lumbar spinal stenosis (LSS) is one of the commonest conditions encountered in spinal surgery, frequently diagnosed when patients start encountering back or leg pain, weakness or changes in sensation. In this article, we shall give a brief overview of what LSS is, what causes it, and how spine surgery can help.

What causes LSS?

If we know that ‘stenosis’ simply means ‘narrowing’, the term ‘lumbar spinal stenosis’ should be somewhat easier to understand: a narrowing of the bony canal in the backbones of the lower spine. The physical cause of the narrowing can be either one of the following, or a combination of them:

• growth of bony spurs known as osteophytes within the spinal canal
• backward bulging of the intervertebral discs into the spinal canal space
• slipping of one of the vertebrae either forwards or backwards (known as spondylolisthesis)
• inflammatory changes occurring in rheumatological conditions that affect the joints, such as ankylosing spondylitis
• proliferation of scar tissue after previous spinal surgery.

Any of these factors can cause compression of the nerves. Since a nerve becomes irritated when compressed, a range of symptoms can result from LSS, which will be discussed in the next section.

What can a patient with LSS experience?

If the nerves become compressed in LSS, the patient may start gradually experiencing several symptoms, but LSS can also commonly be noted by chance if a patient happens to have a scan taken for a different reason. Since the anatomy of the nerves in the lumbar spine differs between individuals, not all patients with LSS have the same experience. The degree of narrowing varies from mild to moderate to severe and can progress from one end of the spectrum to the other due to a variety of factors.

One of the commonest symptoms reported by patients with LSS is lower back pain, which is not actually due to the compressed nerves but rather the degeneration (or ‘wear and tear’) of the articular facets or intervertebral discs.

The typical symptoms attributable to LSS causing nerve compression include pain of a ‘shooting’ or ‘burning’ character, which may spread into the buttocks or legs and may be worse on one side of the body.

It is important to note that patients often find that certain postures — such as lying, sitting, leaning in a particular direction, or standing — have a variable effect on the pain. Patients

typically may report that the symptoms in the legs (e.g. aching, tiredness, pins and needles) get worse after walking a certain distance and improve after resting for some time or leaning forwards. Patients often must stop and start — this is known as neurogenic claudication. It is important to consider that a similar set of symptoms can occur when there is disease of the leg arteries leading to poor blood flow, meaning that the patient may initially be investigated by vascular surgeons for arterial disease.

Since the nerves from the lumbar nerves carry both movement signals and sensory signals, the patient may occasionally notice decreased strength in the muscles of the leg and foot, and areas of abnormal skin sensation, such as numbness or pins-and-needles-type tingling. Bladder, bowel and sexual function are all controlled by nerves originating in the lumbar region too, meaning that patients with LSS can sometimes report symptoms relating to impaired control of urination, defecation and sexual function (e.g. erectile dysfunction) if the nerve entrapment is severe, and surgeons often ask patients to watch out for these.

How can spinal surgery help in LSS?

The first steps before considering an operation to relieve LSS pain are non-surgical. The following may be sufficient to control pain:

• simple painkillers (e.g. paracetamol and ibuprofen)
• stronger medications such as pregabalin, gabapentin or amitryptiline (which can be prescribed by the GP)
• physiotherapy
• complementary therapies.

It is perhaps important to note that injections of medication into the spine have been shown to be ineffective for LSS pain.

The principle underlying surgery for LSS is to reduce the narrowing of the spinal canal, creating more space for the nerves to pass through without being compressed. The main part of the operation is often removal of all or part of the lamina (see part of the bone highlighted in red in the diagrams). Different terms are used by spine surgeons depending on how much bone is removed:

• laminotomy (if a small part of the lamina is removed)
• hemilaminectomy (if only one side of the lamina is removed, leaving the spinous process intact)
• laminectomy (if the entire lamina and spinous process is removed).

Regardless of the method adopted, the aim is to achieve adequate decompression of the nerves without surgically causing spinal instability. Decompression is also achieved by drilling away excess bone on the underside of the articular facet and overgrown ligament from around the spinal canal (these are changes frequently arising as a result of age-associated ‘wear and tear’).

If the LSS is accompanied by poor alignment of the backbones (also known as spondylolisthesis), a procedure known as a lumbar inter-body fusion may be preferred, although not always so. Here, the surgeon inserts a combination of screws, rods or cages to stabilise the lumbar spine by fusing neighbouring vertebrae together. The number of vertebrae fused will depend on the levels which are worst affected by LSS.

Summary

Lumbar spinal stenosis is a common spinal condition associated with age, in which the patient may experience a combination of lower back and leg pain with possible weakness, abnormal skin sensation and changes to bladder, bowel and sexual function. A variety of surgical procedures may be performed on the spine to relieve the symptoms associated with LSS.

Written by A. M. H. Gebreyohanes

Content reviewed for accuracy by Mr Parag Sayal (consultant spinal neurosurgeon at the National Hospital for Neurology and Neurosurgery, Queen Square)