Last revised by Jay Gajera on 14 Dec 2023

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 may be the cause of low back pain in ~50% of adolescent athletes 7.

Spondylolysis may be developmental or acquired. Developmental defects may develop in patients <10 years 7. Acquired defects have two main mechanisms:

  • repeated microtrauma, resulting in a stress injury and eventual fracture of the pars interarticularis; a dysplastic pars is usually present

  • 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 the L4 level 1,2

  • unilateral or bilateral

Imaging features depend on the age of the lesion. CT is considered the gold standard although MRI should be used as the first-line imaging modality in adolescents 7.

  • 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

The Hollenberg classification system is based on MRI features but correlates well with SPECT-CT 6,7:

  • grade 0: normal pars interarticularis; MRI: no signal abnormality, pars interarticularis intact

  • grade I: stress reaction; MRI: marrow edema; intact cortical margins

  • grade II: incomplete stress fracture; MRI: marrow edema; incomplete cortical fracture or fissure

  • grade III: acute complete stress fracture; MRI: marrow edema; complete cortical fracture extending through pars interarticularis

  • grade IV: chronic stress fracture; MRI: no marrow edema; fractures completely extending through pars interarticularis

Surgery is only considered in rare circumstances as most cases respond to conservative management 2. Incomplete fractures demonstrate good healing rates with conservative management 7.

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