MRI Evaluation of Paraspinal Muscle Thickness and Interspinous Gap at the Lumbar Level: A Retrospective Cross-sectional Study.

Background: The erector spinae (ES), one of the paraspinal muscles, is important in invasive procedures performed on the lumbar spine. There are a few data on magnetic resonance imaging (MRI) of this muscle and interspinous gap (ISG). This study aimed to measure bilateral ES thickness at L4-5 and L5-S1 levels, and ISG at L4-5 level in lumbar MRI. Methods: Between May 2020 and 2021, patients who presented with complaints of low back pain and underwent lumbar MRI with the preliminary diagnosis of piriformis syndrome were retrospectively scanned. This syndrome was chosen to ideally evaluate paraspinal muscle dimensions in a population without disc herniation. A total of 408 cases (225 males and 183 females) without disc herniation were identified, and ES muscles (REST, LEST, and AEST) and ISG measurements were performed via picture archiving and communication systems (PACS). Results: At the L4-5 level, mean REST was 40.11 ± 4.46 mm, mean LEST was 39.83 ± 4.57 mm and AEST was 39.97 ± 4.51 mm. There was no statistical difference according to gender and age ( Conclusion: The identification and thickness measurement of paraspinal muscles are important in lumbar surgical interventions. For the first time, ES muscle thickness and ISG were evaluated in routine lumbar MRI scans, and valuable data that could contribute to the literature were obtained only with the use of PACS.