Lumbar disc disease accounts for a large amount of lost productivity in the workforce. Accurate diagnosis can be difficult and often requires interpretation. Treatment is controversial. Treatment failures are not uncommon, are often related to posttraumatic or work-related injuries, and may result in litigation. As a consequence, this disease can generate distrust of physicians on the part of patients and vice versa. Surgical treatment was not widespread until the 1950s. Today, lumbar discectomy is one of the most commonly performed elective operations in the United States.

  • Epidemiology
    • 95% involve L4/5 or L5/S1 levels
      • L5/S1 most common level
    • peak incidence is 4th and 5th decades
    • only ~5% become symptomatic
    • 3:1 male:female ratio
  • Pathoanatomy
    • recurrent torsional strain leads to tears of outer annulus   which leads to herniation of nucleus pulposis
  • Prognosis
    • 90% of patients will have improvement of symptoms within 3 months with nonoperative care.
    • size of herniation decreases over time (reabsorbed) 
      • sequestered disc herniations show the greatest degree of spontaneous reabsorption
      • macrophage phagocytosis is mechanism of reabsorption
Anatomy
  • Complete intervertebral disc anatomy and biomechanics 
  • Disc composition
    • annulus fibrosis
      • composed of type I collagen, water, and proteoglycans  
      • characterized by extensibility and tensile strength
        • high collagen / low proteoglycan ratio (low % dry weight of proteoglycans) 
    • nucleus pulposus
      • composed of type II collagen, water, and proteoglycans
      • characterized by compressibility
        • low collagen / high proteoglycan ratio (high % dry weight of proteoglycans) 
          • proteoglycans interact with water and resist compression
        •  a hydrated gel due to high polysacharide content and high water content (88%)
  • Nerve root anatomy
    • key difference between cervical and lumbar spine is 
      • pedicle/nerve root mismatch
        • cervical spine C6 nerve root travels under C5 pedicle (mismatch)
        • lumbar spine L5 nerve root travels under L5 pedicle (match)
        • extra C8 nerve root (no C8 pedicle) allows transition
      • horizontal (cervical) vs. vertical (lumbar) anatomy of nerve root
        • because of vertical anatomy of lumbar nerve root a paracentral and foraminal disc will affect different nerve roots
        • because of horizontal anatomy of cervical nerve root a central and foraminal disc will affect the same nerve root