Thoracolumbar Fascia Microstructure and Low Back Pain: Insights From Quantitative Ultrasound Homodyned K-Distribution Statistical Modeling

To compare the thoracolumbar fascia (TLF) microstructure between individuals with and without nonspecific low back pain (NSLBP) using homodyned K-distribution (HKD) statistical modeling of the ultrasound radiofrequency signal. In this prospective ancillary analysis of a clinical trial (February 2021-June 2022), we included 29 NSLBP participants (18 women; mean age, 57 ± 10 y; range 40-73) and 31 asymptomatic controls (22 women; mean age 52 ± 10 y; range 38-74; p = 0.04). TLF ultrasound images were analyzed for three HKD parameters: mean intensity normalized by the maximum intensity (μn), reciprocal of the scattering cluster parameter (1/α), and diffuse-to-total signal power ratio (1/(κ+1)). Statistical tests included the Student t-test, Mann-Whitney U test, and a linear mixed-effects regression model. The 1/α value was lower in NSLBP patients (0.71 ± 0.18) compared to controls (0.77 ± 0.19; p = 0.003). The 1/(κ+1) parameter was also reduced in NSLBP patients (0.34 ± 0.07) versus controls (0.35 ± 0.08; p = 0.046). No significant difference in μn was observed between groups (p = 0.996). Regression analysis showed that NSLBP was associated with lower 1/α and 1/(κ+1) (p = 0.048 each). Sex influenced 1/(κ+1) (p = 0.01) and μn (p = 0.0004), with women having lower 1/(κ+1) and higher μn. The depth of the region of interest was significantly predicted 1/α (p < 0.001). Quantitative ultrasound detected microstructural alterations in the TLF of NSLBP patients compared to controls, with notable sex differences in tissue properties. Clinicaltrials.gov, NCT04716101. Registered 14 January 2021, https://clinicaltrials.gov/study/NCT04716101.