Comparison of differences and random errors in pedicle diameter measurements between MRI and CT: observational study of 315 pedicles in Lenke type 1 adolescent idiopathic scoliosis patients.

Background Context: Posterior spinal fusion with pedicle screws is commonly used for the treatment of adolescent idiopathic scoliosis (AIS). To reduce radiation exposure, methods other than computed tomography (CT) are desirable for preoperative determination of pedicle diameter.
Purpose: Investigate the differences between magnetic resonance imaging (MRI) and CT measurements of pedicle diameter.
Study Design: Cross-sectional research.
Patient Sample: Twenty-one AIS Lenke type 1 patients (19 female and 2 males, mean age at surgery: 15.4 years) who underwent posterior spinal fusion between April 2009 and October 2019.
Outcome Measures: Gap between CT and MRI pedicle diameters.
Methods: The inner and outer diameters of the right and left pedicles from T1 to L3 were measured separately by two spine surgeons for statistical comparisons.
Results: The respective minimum and maximum CT-MRI values were -3.7 mm and 4.7 mm for inner diameter and -4.6 mm and 5.3 mm for outer diameter. Regarding inter-examiner error, the probability of a 2 mm difference in measurement was less than 5% for both modalities. The probability of a 1 mm difference was also less than 5%, and that of a 3 mm or more difference was 2.1% for the inner diameter and 2.9% for the outer diameter. Whereas low body weight was significantly associated with measurement differences, pedicle laterality was not.
Conclusions: MRI does not have the reliability to measure pedicle size in AIS patients at present. However, with advancements in image processing technology, the accuracy of pedicle size measurement by MRI may soon improve.
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