Geography of Lumbar Paravertebral Muscle Fatty Infiltration

Study Design. Cross-sectional. Objective. We quantified fatty infiltration (FI) geography of the lumbar spine to identify whether demographics, temporal low back pain (LBP), and disability influence FI patterns. Summary of Background Data. Lumbar paravertebral muscle FI has been associated with age, sex, LBP, and disability; yet, FI accumulation patterns are inadequately described to optimize interventions. Methods. This cross-sectional study employed lumbar axial T1-weighted magnetic resonance imaging in 107 Southern-Chinese adults (54 females, 53 males). Single-slices at the vertebral inferior end-plate per lumbar level were measured for quartiled-FI, and analyzed against demographics, LBP, and disability (Oswestry Disability Index). Results. Mean FI% was higher in females, on the right, increased per level caudally, and from medial to lateral in men ( P < 0.05). FI linearly increased with age for both sexes ( P < 0.01) and was notably higher at L 4&5 than L1, 2&3 for cases aged 40 to 65 years. BMI and FI were unrelated in females and inversely in males ( P < 0.001). Females with LBP week and males with LBP year had 1.7% (each) less average FI ( P < 0.05) than those without pain at that time-point. Men locating their LBP in the back had less FI than those without pain ( P < 0.001). Disability was unrelated to FI for both sexes ( P > 0.05). Conclusion. Lumbar paravertebral muscle FI predominates in the lower lumbar spine, notably for those aged 40 to 65, and depends more on sagittal than transverse distribution. Higher FI in females and differences of mean FI between sexes for BMI, LBP, and disabling Oswestry Disability Index suggest sex-differential accumulation patterns. Our study contradicts pain models rationalizing lumbar muscle FI and may reflect a normative sex-dependent feature of the natural history of lumbar paravertebral muscles. Level of Evidence: 2