Lumbar spinal stenosis (LSS) is a narrowing of the spinal canal. Though LSS may occasionally occur congenitally with symptoms presenting in the thirties and forties, by far the largest number of patients with LSS acquire the disease later in life and are over 60 years of age. The spinal canal is narrowed as a result of degenerative changes. It is estimated that as many as 400,000 Americans may suffer from this disease the majority of which have not been diagnosed. The treatment is a decompressive lumbar laminectomy.

Anatomy

• The lumbar spine and pelvis, the low back, supports the entire body. The lumbar spine allows bending forward and backward and to twist at the waist
  
• The normal lumbar spine is composed of five building blocks called vertebrae that sit on the sacrum, which is the back part of the pelvic bone. (Figure 1)
  
• Each vertebra is constructed of a body, lamina, and pedicles, which surround an opening, the spinal canal.(Figure 2)
  
• A spinous process extends posteriorly (towards the back) from the lamina in the midline. Through the spinal canal pass the nerve roots that emerge from the end of the spinal cord and go to form the nerves to the legs. (Figure 3)
  
• Each root exits the spinal canal through a 'hole' in the side of the canal formed by two adjacent vertebrae called a foramen
  
• The roots float in fluid and are contained within a fibrous sac called the dura
  
• Separating any two vertebral bodies is a soft elastic material called a disk. The disk is composed of two parts, a soft center called the nucleus and a tough outer band called the annulus. (Figure 4). There are five lumbar disks
  
• On each side of the back of the spinal canal and linking one vertebra to the next are a series of small joints called facets
  

Figure 1 - The lumbar spine is composed of five vertebra separated by disks.	Figure 2 - Cross-section of a lumbar vertebrae showing the various parts.