Chronicity and physical activity levels independently associate with spatial patterns of multifidus fat infiltration...

This study sought to identify spatial patterns of elevated fat infiltration (FI) in the multifidus associated with chronic low back pain (cLBP) chronicity (duration) and physical activity levels.

On 223 cLBP patients, we mapped the FI distribution in the multifidus at L4L5 and L5S1 using 3T MRI and advanced sequences (IDEAL). Using statistical parametric mapping, we identified FI patterns independently associated with increased cLBP chronicity and decreased physical activity levels. Then, we used linear mixed-effects modeling to identify associations between cLBP chronicity, physical activity level and two FI measures, the FI% of the entire muscle cross-sectional area (overall FI%) and the FI% in the deepest 15% of the MF (deep15 FI%).

Increased cLBP chronicity associated with elevated FI in the deepest 24% of the MF at L4L5 (p < .01) and in the superficial region of the MF at L4L5 (p < .05) and L5S1 (p < .05). Lower levels of physical activity associated with higher MF FI in the deepest 10% of the MF at L4L5 (p < .05). We also find that increased cLBP chronicity (p < .01) and lower physical activity levels (p < .05) associated with elevated deep15 FI%, independent of age, disc degeneration, and pain severity.

Increased cLBP chronicity and lower physical activity levels independently associate with elevated MF FI. Further, these associations are independent of age, disc degeneration, and pain severity. Lastly, physical activity may have an independent association with MF FI specific to the deep MF, where fat infiltration has been shown to associate with cLBP symptoms and adjacent disc degeneration.