• Spondylolysis:
    • Bony defect at the pars interarticularis (the isthmus of bone between the superior and inferior facets)
    • Can be unilateral or bilateral
    • Bilateral form has a much higher likelihood of slippage or spondylolisthesis than the unilateral form
    • Occurs at L5 85–95% of the time. Occurs at L4 5–15% of the time. Rarely higher up to the L1 level
    • 4% multilevel involvement
    • More common than spondylolisthesis
  • Spondylolisthesis:
    • The slipping forward of 1 vertebra upon another
    • Spondylolysis can contribute to spondylolisthesis, which is noted in ∼5% of the population. Gender differences are debated but likely less disparate than originally thought with nearly equal rates
    • Of those with spondylolysis, 50% will have some degree of spondylolisthesis development during their lifetime, and 50% of those will be symptomatic:
    • Literature does not associate athletic activity with increased slippage
    • Spondylolisthesis predisposes to nerve root impingement and frequently sciatica
  • Classification:
    • Type 1 – dysplastic: Congenital defect of the neural arch or intra-articular facets is often associated with spina bifida occulta
    • Type 2 – isthmic: Stress fracture from repetitive microtrauma through the neural arch
    • Type 3 – degenerative: Long-standing segmental instability
    • Type 4 – traumatic
    • Type 5 – pathologic: Generalized or focal bone disease
    • Type 1 has the highest risk of progression ∼32% when sports related; isthmic – only 4% risk
    • Spondylolisthesis is divided into 4 grades based on degree of slippage (Meyerding grading system):
      • Grade I: Up to 25% of the vertebral body width
      • Grade II: 26–50% of vertebral body width
      • Grade III: 51–75% of vertebral body width
      • Grade IV: 76–100% of vertebral body width
    • The most common location for spondylolisthesis is L5 displaced on the sacrum (85–95%), followed by L4 on L5

Pediatric Considerations
  • Spondylolysis is one of the most common causes of serious low back pain in children, although it is most often asymptomatic
  • Symptoms most often present during adolescent growth spurt from age 10–15 yr
  • Seen commonly in athletic teens; particularly in sports involving back hyperextension (e.g., gymnastics, diving, football)
  • Acute symptoms are related to trauma


Unknown; theories include congenital pars anomalies, alterations in bone density, and recurrent subclinical stress injury

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