CHAPTER 10: Imaging the Lumbar Spine

1. INTRODUCTION: FAST LUMBAR SPINE FACTS

❑ Traumatic Injuries

• The most commonly injured levels in the lower spine are in the thoracolumbar (T11, T12, L1, L2) vertebrae. These segments are predisposed to mechanical forces because they are the transitional areas between the relatively fixed thoracic spine and the more mobile lumbar spine. Forces often dissipate here.

• Compression fractures and fracture–dislocations occur with highest frequency at T12 and L1 and 15% to 20% of these involve neurological injury.

• Spondylolysis is a defect at the pars interarticularis, which may be traumatic or congenital (rare) or owing to a stress fracture from chronic strain. It is seen in athletes in sports with repetitive hyperextension and rotation, such as diving, gymnastics, volleyball, and in weight lifting and football.

❑ Pathologies

• Spondylolisthesis is the forward slippage of one vertebra on the stationary vertebra below it. A synonymous term is anterolisthesis. L4–L5 and L5–S1 are most often involved owing to the predisposition of the lumbosacral angle to ligamentous laxity and degenerative disk changes. Increased athletic activity in adolescence or heavy labor in adulthood is often an instigating factor.

• Spinal stenosis is the constriction of the spinal canal owing to degenerative soft tissue and bone enlargement. Mild stenosis is asymptomatic. Moderate stenosis presents with varying degrees of vascular and neurogenic compression symptoms. Severe stenosis can cause cauda equina syndrome.

• Intervertebral disk herniation is an abnormal extension of the nucleus pulposus through the annulus fibrosis and beyond adjacent vertebral margins. Most herniations occur at L4–L5, are common in the 25-to-45-year age group, and affect men more often than women. It is also now recognized that a large percentage of the asymptomatic population has disk bulging or focal herniations verified on MR or CT. Herniations can occur

  • ◗ Anteriorly, elevating the anterior longitudinal ligament and producing osteophytes at the vertebral joint margins

  • ◗ Intravertebrally, protruding into adjacent vertebral bodies through a weakened endplate, producing a small osseous cavity or Schmorl's node

  • ◗ Posteriorly/posterolaterally, compressing the spinal nerve or thecal sac and causing low back and radiating leg pain. Usually, only these herniations produce symptoms.

    • Note: Most patients with diskogenic pain patterns improve in 4 to 6 weeks, and no imaging is recommended during this time. Why? Imaging done in an acute episode may reveal preexisting abnormalities that are not related to the current acute episode. This information may confuse the situation, eliminate chances for conservative management, and instigate premature or unnecessary surgical consultation.

❑ The Imaging Choices

• Radiographs are the initial imaging study for lumbar spine problems, with the exception of high-risk trauma patients, who are evaluated by CT. However, if CT is not available, radiographs are indicated.

• Computed tomography (CT) is the initial imaging study for high-risk trauma patients. One scan can evaluate for multi-system trauma: the head CT for the brain, the thoracic-abdominal-pelvic (TAP) scan ...