The Spine Journal 26 (2026) 106−118
This clinical study maps spatial fat infiltration (FI) within the lumbar multifidus (MF) of 230 chronic low back pain (cLBP) patients using 3T IDEAL MRI and statistical parametric mapping to identify level- and region-specific FI patterns. The authors introduce a novel “fat-map” method and define a deep15 FI% (deepest 15% of MF) to compare regional FI with overall whole‑muscle FI across L1L2–L5S1.
Key results show elevated FI in the deep MF at L4L5 and L5S1 is associated with higher pain (PEG scores) and adjacent disc degeneration independent of age, sex, and BMI, while overall FI% is more strongly linked to demographic factors. The deep15 FI% emerges as a potential biomarker for cLBP, suggesting regional MF degeneration may better explain pain mechanisms than whole‑muscle summary measures.
Deep multifidus fat infiltration (FI): Elevated fat content in the deepest regions (deepest 15%) of the multifidus muscle at the lower lumbar spine (L4L5, L5S1) is more strongly associated with chronic low back pain (cLBP) symptoms and adjacent disc degeneration than overall muscle FI%.
Regional specificity: FI in the deep multifidus at lower lumbar levels is less influenced by age, sex, and BMI compared to overall FI%, making it a more specific biomarker for cLBP.
Novel biomarker (deep15 FI%): The “deep15 FI%” (mean fat fraction in the deepest 15% of the multifidus at L4L5/L5S1) is a regionally specific muscle quality measure, showing a stronger association with pain and disc degeneration than traditional whole-muscle FI% measures.
Demographic factors: Older age and female sex are associated with increased FI throughout the multifidus, while higher BMI mainly affects FI in the superficial 60% of the muscle, not the deep region at lower lumbar levels.
Pain association: Higher deep15 FI% at the lower lumbar levels is significantly associated with higher pain and pain interference scores (PEG survey), while overall FI% is not.
Disc degeneration link: Adjacent disc degeneration is the only degenerative spine feature consistently associated with increased deep multifidus FI at lower lumbar levels; other features (e.g., Modic changes, facet osteoarthritis) do not show this association when controlling for age, sex, and BMI.
Clinical implications: Deep multifidus FI could serve as a more precise imaging biomarker for cLBP and may guide future targeted interventions, though further longitudinal and interventional studies are needed to confirm causality and reversibility.
Limitations: The study’s spatial FI analysis is limited to radial (deep-to-superficial) direction and cross-sectional design; further research is needed to clarify causal mechanisms and intervention effects.
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