Spondylolysis

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.

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 stress fracture of the pars interarticularis. A dysplastic pars is usually present. Genetics are also believed to be a factor. It is more common in men than in women 1.

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

Location
  • ~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
Associations
  • ~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.

Plain radiograph
  • 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
CT/MRI
  • wide-canal sign may be present on sagittal images when there is spondlyolisthesis 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

Share article

Article information

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

Support Radiopaedia and see fewer ads

Cases and figures

  • Drag
    Case 1
    Drag here to reorder.
  • Drag
     Case 2
    Drag here to reorder.
  • Drag
    Case 3
    Drag here to reorder.
  • Drag
    Case 4
    Drag here to reorder.
  • Drag
    Case 5
    Drag here to reorder.
  • Drag
    Lateral projectio...
    Case 6: L3 with spondylolisthesis
    Drag here to reorder.
  • Drag
    Case 7: on MRI
    Drag here to reorder.
  • Updating… Please wait.
    Loadinganimation

    Alert accept

    Error Unable to process the form. Check for errors and try again.

    Alert accept Thank you for updating your details.