Dr Henry Knipe and Radswiki et al.

Spondylolysis is a defect in the pars interarticularis of the neural arch, the portion of the neural arch that connects the superior and inferior articular facets. It is commonly known as pars interarticularis defect or more simply as pars defect

Spondylolysis is present in ~5% of the population 2 and higher in the adolescent athletic population.  It is more common in men than in women 1.

Spondylolysis is commonly asymptomatic. Symptomatic patients often have pain with extension and/or rotation of the lumbar spine. Approximately 25% of individuals with spondylolysis have symptoms at some time.

It is a common cause of low back pain in adolescents and in particular athletes. 

Spondylolysis is believed to be caused by repeated microtrauma, resulting in a stress fracture of the pars interarticularis. A dysplastic pars is usually present. Genetics are also believed to be a factor.

Traumatic pars defects result from high-energy trauma where there is hyperextension of the lumbar spine and are rare in a congenitally normal vertebra.

  • ~90% of cases of spondylolysis occur at the L5 level and ~10% occur at L4 level 1,2
  • the process may be unilateral or bilateral
  • ~65% of patients with spondylolysis will progress to spondylolisthesis 2, which is seen radiographically in ~25% 4 In most patients this occurs before the age of 16.
  • spina bifida occulta

Imaging features depend on the age of the lesion.

  • limited sensitivity compared to SPECT and CT 4
  • Scotty dog sign: on oblique radiographs, a break in the pars interarticularis can have the appearance of a collar around the dog's neck
  • inverted Napoleon hat sign
  • wide-canal sign may be present on sagittal images when there is spondylolisthesis 3
  • deviation of the spinous process
  • sclerosis of the contralateral pedicle

Surgery is only considered in rare circumstances as most cases respond to conservative management 2


Article information

rID: 12262
Synonyms or Alternate Spellings:
  • Pars defect
  • Pars interarticularis defect

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Cases and figures

  • Case 1
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  •  Case 2
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  • Case 3
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  • Case 4
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  • Case 5
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  • Case 6: L3 with spondylolisthesis
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  • Case 7: on MRI
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  • Case 8: multilevel
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  • Case 9: on T1 VIBE sequence
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