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.
- ~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 spondlyolisthesis 3
- deviation of the spinous process
- sclerosis of the contralateral pedicle
Treatment and prognosis
Surgery is only considered in rare circumstances as most cases respond to conservative management 2.
- 1. Jinkins JR, Matthes JC, Sener RN et-al. Spondylolysis, spondylolisthesis, and associated nerve root entrapment in the lumbosacral spine: MR evaluation. AJR Am J Roentgenol. 1992;159 (4): 799-803. AJR Am J Roentgenol (abstract) - Pubmed citation
- 2. Syrmou E, Tsitsopoulos PP, Marinopoulos D et-al. Spondylolysis: a review and reappraisal. Hippokratia. 2010;14 (1): 17-21. Free text at pubmed - Pubmed citation
- 3. Ulmer JL, Mathews VP, Elster AD et-al. Lumbar spondylolysis without spondylolisthesis: recognition of isolated posterior element subluxation on sagittal MR. AJNR Am J Neuroradiol. 1995;16 (7): 1393-8. Pubmed citation
- 4. Standaert C. British Journal of Sports Medicine.34 (6): . doi:10.1136/bjsm.34.6.415