What is the role of MRI 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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MRI has not been studied as well as plain radiography, radionuclide scanning, and CT scanning. Initial studies revealed that MRI provides great difficulty in identifying a normal intact pars interarticularis, resulting in a low positive predictive value.

MRI may be useful in detecting spondylolysis earlier in the clinical course than plain radiography or CT scanning does; this makes MRI comparable to radionuclide scanning, whereas removing the disadvantages of radiation exposure. In 1993, a study evaluating MRI findings in pars interarticularis injury using a 0.5-T magnet suggested that MRI may show a hypointense area in the pars interarticularis area on T1-weighted images prior to the appearance of spondylolysis being visible on plain radiographs or CT scans. This study went on to explain that prior literature suggested that the hypointense area may be due to hemorrhage in the pars interarticularis area or edema of adjacent tissues and that hemorrhage appears hypointense on T1-weighted images owing to the presence of deoxyhemoglobin. [50]

Goda et al conducted a study that included 98 adolescent patients to investigate the discrepancy between MRI and computed tomography (CT) findings in the spinal level distribution of spondylolysis. The authors concluded that MRI revealed a higher prevalence of L3 or L4 spondylolysis than observed with CT. [51]

Improvements in the technical aspects of MRI have increased its usefulness in imaging pars interarticularis lesions. T1-weighted imaging with sagittal 3-mm slices has been shown to be most useful. Kobayashi et al published a study that assessed MRI with a 0.3-T magnet to evaluate for spondylolysis in patients who did not have clear spondylolysis diagnosed with plain radiographs. MRI showed active spondylolysis in 45.7% of the patients with negative findings on plain radiographs and in 91.7% of patients with unclear findings on plain radiographs. [52] They used a 5-stage classification system based on CT findings, and 70.6% of the pars injuries were in the nonlysis or very early stage, again confirming that MRI may be useful in detecting spondylosis earlier than plain radiography or CT scanning. [52]

MRI offers some advantages; this modality is the criterion standard of imaging in most other lumbosacral spine pathologies. The lack of ionizing radiation makes MRI especially attractive for use on adolescent athletes. A study comparing MRI findings found prevalent abnormalities of the lumbar spine in adolescents who were high-performance rowers; these abnormalities included disk disease and pars interarticularis stress reaction. [53]

The overall role of MRI has yet to be determined, as it is not clearly defined in the literature at this point. MRI is not a first-line imaging study in clinically suggested spondylolysis, but rather it is an adjunct study in evaluating for alternative pathologies (see Differentials).

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