Lower Back Issues

Lumbar Spinal Stenosis

Causes
In the lumbar spine, the spinal canal usually has more than enough room for the spinal nerves. The canal is normally 17 to 18 millimeters around, slightly smaller than a penny. Spinal stenosis develops when the canal shrinks to 12 millimeters or less. When the size drops below 10 millimeters, severe symptoms of lumbar spinal stenosis occur.

There are many reasons why symptoms of spinal stenosis develop. Some of the more common reasons include:

  • congenital stenosis (being born with a small spinal canal)
  • spinal degeneration
  • spinal instability
  • disc herniation

Congenital stenosis: Some people are born with (congenital) a spinal canal that is narrower than normal. They may not feel problems early in life. However, having a narrow spinal canal puts them at risk for stenosis. Even a minor back injury can cause pressure against the spinal cord. People born with a narrow spinal canal often have problems later in life, because the canal tends to become narrower due to the effects of aging.

Degeneration: Degeneration is the most common cause of spinal stenosis. Wear and tear on the spine from aging and from repeated stresses and strains can cause many problems in the lumbar spine. The inter-vertebral disc can begin to collapse, and the space between each vertebrae shrinks. Bone spurs may form that stick into the spinal canal and reduce the space available to the spinal nerves. The ligaments that hold the vertebrae together may thicken and also push into the spinal canal. All of these conditions cause the spinal canal to narrow.

Spinal instability: Spinal instability can cause spinal stenosis. Spinal instability means that the bones of the spine move more than they should. Instability in the lumbar spine can develop if the supporting ligaments have been stretched or torn from a severe back injury. People with diseases that loosen their connective tissues may also have spinal instability. Whatever the cause, extra movement in the bones of the spine can lead to spinal stenosis.

Disc herniation: Spinal stenosis can occur when an intervertebral disc in the low back herniates (ruptures). Normally, the shock-absorbing disc is able to handle the downward pressure of gravity and the strain from daily activities. However, if the pressure on the disc is too strong, such as landing from a fall in a sitting position, the nucleus inside the disc may rupture through the outer annulus and squeeze out of the disc. This is called a disc herniation. If an intervertebral disc herniates straight backward, it can press againstthe nerves in the spinal canal, causing symptoms of spinal stenosis.

Symptoms
Spinal stenosis usually develops slowly over a long period of time. This is because the main cause of spinal stenosis is spinal degeneration in later life. Symptoms rarely develop quickly when degeneration is the source of the problem. A severe injury or a herniated disc may cause symptoms to develop immediately.

Patients with stenosis don’t always feel back pain. Primarily, they have severe pain and weakness in their legs, usually in both legs at the same time. Some people say they feel that their legs are going to give out on them.

Symptoms mainly affect sensation in the lower limbs. Nerve pressure from stenosis can cause a feeling ofpins and needles in the skin where the spinal nerves travel. Reflexes become slowed. Some patients report charley horses in their leg muscles. Others report strange sensations like water trickling down their legs.

Symptoms change with the position of the low back. Flexion (bending forward) widens the spinal canal and usually eases symptoms. That’s why people with stenosis tend to get relief when they sit down or curl up to sleep. Activities such as reaching up, standing, and walking require the spine to straighten or even extend (bend back slightly). This position of the low back makes the spinal canal smaller and often worsens symptoms.