Study Design. 

A retrospective comparative study.

Objective. 

The aim of this study was to compare the length and diameter of thoracic pedicles in patients with adolescent idiopathic scoliosis (AIS) as measured on preoperative magnetic resonance imaging (pMRI) to intraoperative computed tomography (iCT) scan.

Summary of Background Data. 

Optimally sized pedicle screw placement during instrumented posterior spinal fusion for AIS can maximize correction and minimize screw pullout. While iCT-guided navigation can quickly estimate screw position and size, this technology is not universally available. Many surgeons utilize pMRI, when obtained, to estimate screw sizes. Data comparing these measurements on pMRI and iCT is limited. We hypothesized that in patients with surgical magnitude AIS, pedicle length, and diameter measured on pMRI would have at least moderate reliability compared to those made on iCT images.

Materials and Methods. 

The pMRI and iCT for 60 patients with structural thoracic curves who underwent posterior spinal fusion for AIS at a single center between 2009 and 2017 were analyzed. Bilateral T5–T12 vertebral levels were evaluated for pedicle chord length and pedicle isthmic diameter on both pMRI and iCT. Between-study reliability and interrater reliability was evaluated for each level of the thoracic spine.

Results. 

There is good reliability for pedicle length [intraclass correlation coefficient (ICC)=0.8, 95% confidence interval (CI): 0.78–0.83] and diameter (ICC=0.86, 95% CI: 0.84–0.88) between pMRI and iCT. When assessed by level, T6 has the lowest reliability for length (ICC=0.52, 95% CI: 0.33–0.67) and diameter (ICC=0.55, 95% CI: 0.35–0.69). Interrater reliability ranged from moderate-to-good reliability for all pedicle measurements for both length and diameter on pMRI and iCT.

Conclusion. 

Pedicle measurements made on pMRI may be used with reasonable reliability to predict pedicle dimensions visualized on iCT, allowing surgeons to preoperatively plan pedicle screw sizes based off magnetic resonance imaging.