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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.
~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
idiopathic scoliosis: ~5% 8
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
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
Treatment and prognosis
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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