Purpose or Learning Objective: Spondylolysis is a defect in the pars interarticularis of the vertebrae, most commonly
the lumbar vertebrae. It is seen in 3 to 10% of adults and can be diagnosed on radiographs,
magnetic resonance imaging (T1 volumetric interpolated breath-hold examination), computed
tomography (CT), or single-photon emission computed tomography. These defects are
common in athletes, particularly in gymnasts, cricketers, footballers, and weight
lifters. A pars defect is a sequela of repetitive stress. The maximum stress occurs
at the L5–S1 level. We hypothesize that the orientation of the pars interarticularis
in relation to the vertebral body is a key factor contributing to the development
of a pars defect.
Methods or Background: A total of 40 patients < 30 years of age who had CT of the lumbar spine were included
in the study. Patients with instrumentation, trauma, and tumors were excluded. The
angle between the posterior lumbar vertebral body and a line tangential to the posterior
pars interarticularis (sagittal pars angle) was calculated from L2 to L5 by two musculoskeletal
radiologists. The t test was used for statistical analysis.
Results or Findings: Eighteen pars defects were found with an average patient age of 19.1 years (range:
10–29 years; 8 females and 10 males). There were 186 intact pars with an average age
of 17.8 years (range: 7–30 years). A statistically significant increase was observed
in the average sagittal pars angle in patients with pars defects (35.6 degrees) compared
with those with an intact pars interarticularis (17.8 degrees) (P = 0.0001).
Conclusion: A relatively increased sagittal pars angle makes the lumbar vertebrae more prone
to developing a pars defect.
