Association between Lumbar Multifidus Muscle Fat Infiltration and Spinopelvic Alignment in Patients with Lumbar Spinal Canal Stenosis: A Sex-Specific Quantitative Study

Abstract

Introduction: Fat infiltration of the multifidus muscle is associated with low back pain and spinopelvic alignment. However, simple quantitative methods for evaluating multifidus fat infiltration are limited, and sex-specific associations in patients with lumbar spinal canal stenosis (LSCS) remain unclear. This study aimed to introduce a reproducible quantitative magnetic resonance imaging (MRI) signal-based index of multifidus fat infiltration and to clarify its sex-specific association with spinopelvic alignment in patients with LSCS.

Methods: Ninety-five patients with LSCS who were scheduled for surgery were included: 42 males and 53 females. The mean signal value of the multifidus (MSV-Mf) was calculated on T2-weighted MRI by normalizing multifidus signal intensity to retroperitoneal fat signal intensity. Spinopelvic alignment parameters and the psoas area index were evaluated. Correlation and multiple regression analyses were performed separately by sex.

Results: In males, MSV-Mf was significantly correlated with sagittal vertical axis (SVA) (r = 0.52, p < 0.01) and remained significantly associated with SVA after adjustment for age or prognostic nutritional index (p < 0.01). MSV-Mf was not associated with psoas area index. In females, MSV-Mf showed a weak positive trend with SVA (r =0.24, p = 0.08). Although the association between MSV-Mf and SVA was significant in each adjusted model (p = 0.03), the overall regression models did not reach statistical significance. MSV-Mf demonstrated good measurement reliability, with intra-observer and inter-observer intraclass correlation coefficients of 0.84 and 0.79, respectively.

Conclusions: MSV-Mf was independently associated with increased SVA in males, whereas the association in females was weaker and exploratory. MSV-Mf may be a reproducible quantitative MRI signal-based index for assessing multifidus fat infiltration in patients with LSCS.