What is the role of plain radiography in the workup of pars interarticularis injury?

Updated: Jan 22, 2019
  • Author: Gerard A Malanga, MD; Chief Editor: Craig C Young, MD  more...
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Traditionally, plain radiographs have been the hallmark of diagnostic imaging in cases of spondylolysis. The lateral oblique view, in which the pars interarticularis is best visualized, is described as having the appearance of a "Scotty dog." In isthmic spondylolytic lesions, the Scotty dog is described as having the appearance of a "collar" or a "broken neck," which is thought to be a pathognomonic finding. [5] In unilateral pars lesions, the contralateral region may demonstrate sclerosis secondary to the increased stresses in that area. [38]

In studies comparing the different views of plain radiographs, including anteroposterior (AP), lateral, and lateral oblique, 19% of pars interarticularis lesions were identified only on the lateral oblique view. Pierce reported the sensitivity of the AP view to be 32%, of the lateral view to be 75%, and of the lateral oblique view to be 77%. [39] The most sensitive view in one study was found to be the lateral spot view of the lumbosacral junction, which revealed 84% of pars interarticularis lesions.

Limitations of plain radiographs lie in the fact that to be optimally visualized, the lesion should ideally be aligned tangentially to the beam. Spondylolytic lesions are often not aligned within the plane of the standard 45º lateral oblique views. Although most authors support the belief that multiple views of the lumbosacral spine are necessary for optimal visualization of the pars interarticularis on plain radiography, the need for routine oblique radiographs has been questioned with concerns regarding increased radiographic exposure. [40] Additionally, spondylolytic lesions seen on radiographs are often believed to represent an old injury that may not be symptomatic.

Flexion and extension lateral radiographs may be obtained if spondylolisthesis or spine instability is suspected.

Based on a literature review, Tofte et al recommended two-view plain radiography as the initial imaging study in pediatric patients thought to have spondylolysis-related back pain. The recommendation was made based on the modality’s efficacy and relatively low cost, as well as the relatively low amount of radiation exposure involved (7-9 times less effective radiation dose than bone scanning and approximately half of that associated with four-view plain radiography and computed tomography [CT] scanning). [41]

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