Sagittal Pars Angle as a Predictor of the Likelihood of Developing Lumbar Vertebral Pars Defects

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.

Publication History

Article published online:
26 May 2023