Pars Interarticularis Injury Workup

Updated: May 16, 2022
  • Author: Gerard A Malanga, MD; Chief Editor: Craig C Young, MD  more...
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Laboratory Studies

Laboratory studies are not indicated for diagnosing lumbosacral spondylolysis.


Imaging Studies

Plain radiography

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. [6] In unilateral pars lesions, the contralateral region may demonstrate sclerosis secondary to the increased stresses in that area. [40]

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%. [41] 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. [42] 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). [43]

Single-photon emission tomography scan (SPECT)

Radionuclide imaging studies, including planar bone scanning and, more specifically, SPECT bone scanning, have been found to be more sensitive than plain radiography in detecting pars lesions. Several authors comparing planar bone scan versus plain radiographs concluded that planar bone scans could potentially detect pars lesions earlier in the clinical course than could plain radiographs. Furthermore, it appears that bone scanning may be more sensitive in differentiating pain-producing pars lesions from incidentally found lesions.

In a study by Lowe et al, a group of patients found to have spondylolysis on plain films were further imaged with a bone scan. [44] A positive bone scan in each case correlated with the presence of LBP, whereas those with negative bone scans were all without pain. Similar results have been obtained in other studies, and it appears that bone scans may have a role in identifying those cases in which the spondylolytic lesion is the pain generator rather than just an incidental finding.

SPECT scanning has been found to be more sensitive than either plain radiography or planar bone scintigraphy in detecting spondylolysis and has, for the most part, replaced planar bone scanning as the radionuclide imaging study of first choice in suspected pars interarticularis lesions.

Studies carried out that compared plain radiography, planar bone scanning, and SPECT scanning by Bodner et al and Bellah et al, respectively, both found the SPECT scan to be more sensitive compared with the other 2 imaging studies. [45, 46] Furthermore, as with planar bone scans, SPECT scans may be helpful in detecting symptomatic pars lesions from asymptomatic lesions as they can identify metabolically active bone change.

A particularly interesting study comparing the clinical outcome following surgery for pars interarticularis defects with SPECT scanning found that patients who became pain free after surgery have positive preoperative SPECT scans, whereas those in whom pain persisted after surgery had negative preoperative scans. This finding implies that those with negative scans may have been experiencing their symptomatology from a source other than the pars lesion.

A Japanese study was performed to clarify the role of SPECT scans. In this study, plain radiographs and SPECT scans were obtained in young patients (mean age 15.6 y) who had LBP and were clinically suspected of having spondylolysis. This study concluded that the SPECT scan is primarily indicated in patients with no apparent abnormality seen on plain radiograph and/or CT scan and who are still suspected of having spondylolysis from their history and physical examination. A positive study was thought to represent a stress reaction in the pars interarticularis, which may be amenable to rest and immobilization. A negative study at this point strongly suggests that spondylolysis is not the likely source of pain and may warrant further imaging to evaluate for a different pathology that may be causing symptomatology. [47]

Herring and Standaert offer the opinion that considering the relatively high radiation exposure one is subjected to in undergoing multiple views on plain film, along with the increased sensitivity of SPECT scanning, the latter may be the most appropriate choice for the initial screening study. [48] The authors feel with the advantages of SPECT scanning, multiple plain radiographic views as an initial screening tool may not play a role in detecting spondylolytic lesions. [48] In cases in which plain radiographs do reveal pars lesions, SPECT scanning can be helpful in documenting the acuity of injury.

Interpretation of plain radiographs coupled with SPECT scan results

Below, table 1 outlines the interpretation of plain radiographs coupled with SPECT scan results.

Table 1 also offers treatment strategies based on these results, as followed by a British institution. [49] These treatment strategies were outlined in a study conducted jointly by the investigators' orthopedic and radiology departments, who investigated the role of SPECT scanning in the management of patients with back pain and spondylolysis. [49]

Although radionuclide imaging may have increased sensitivity in detecting pars defects compared with plain radiographs, they are not necessarily highly specific for this detection and have been found to yield positive results from pathologies other than spondylolysis, including a infection and tumor such as osteoid osteoma and osteoblastoma.

Table 1. Outline of the Treatment Strategy Based on Results of Plain Radiographs and SPECT Scanning in the Evaluation of Defects of the Pars Interarticularis in Patients Clinically Suspected of Having Symptomatic Pars Interarticularis Lesions (Open Table in a new window)

Plain Radiograph






Pathology other than pars defect should be suspected

Further investigation of cause of back pain should be performed (eg, MRI)



Early pars interarticularis fracture

Conservative management in form of rest, +/– bracing




Conservative management in the form of rest and bracing



Pseudoarthrosis or old unhealed fracture

Consider surgical intervention for stabilization to prevent spondylolisthesis and to relieve pain. Consider further investigation to rule out alternative pathology.

CT scanning

As with the above mentioned radionuclide studies, CT scanning has been found to be more sensitive than plain radiography in visualizing spondylolytic lesions. [50, 51]

In a study comparing plain radiography, CT scanning, and bone scintigraphy (either bone scan or SPECT), CT scanning was found to be more sensitive than plain radiographs, as well as more specific than radionuclide imaging. Both standard axial views and reverse gantry CT imaging were used for this study, and the authors noted that some pars interarticularis defects were seen more clearly with one versus the other, although a direct comparison of views was not made.

CT scanning has the added benefit of providing more detail about the nature of the pars interarticularis defect than bone scanning or SPECT scanning does. CT scanning has the advantage of visualizing other spinal pathologies, most notably intervertebral disc pathology, which is not seen on the other radionuclide imaging studies. The relationship between CT scanning and SPECT scanning has not been fully established, and it is presently unclear as to which is the more sensitive study. The role of CT scanning may be as an adjunctive study investigating the stage of healing in a pars fracture.

Yamane et al described a 4-stage grading system based on CT scan findings: nonlysis, prefissure, fissure, and pseudoarthrosis. [52]


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. [52]

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. [53]

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. [54] 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. [54]

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. [55]

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).