Thoracolumbar fascia ultrasound shear strain differs between low back pain and asymptomatic individuals: expanding the evidence.

Objectives: To compare thoracolumbar fascia (TLF) shear strain between individuals with and without nonspecific low back pain (NSLBP), investigate its correlation with symptoms, and assess a standardized massage technique's impact on TLF shear strain.

Methods: Participants were prospectively enrolled between February 2021 and June 2022. Pre- and post-intervention TLF ultrasound and pain/disability questionnaires were conducted. Cumulated (C|ShS|) and maximum (Max|ShS|) shear strain parameters were computed from radiofrequency data, and TLF thickness was measured on reconstructed B-mode images. Statistical analysis included linear mixed-effects regression.

Results: Thirty-two NSLBP participants (mean age, 57 ± 9 years [standard deviation]; 21 women) and 32 controls (51 ± 10 years; 22 women) (p = 0.02) were enrolled. The mean shear strain was higher in NSLBP participants (C|ShS|: 327.1% ± 106.0 vs 290.2% ± 99.8, p < 0.0001; Max|ShS|: 8.1% ± 2.8 vs 7.0% ± 2.4, p < 0.0001) than controls, while mean TLF thickness (1.6 mm ± 1.0 vs 1.5 mm ± 0.9; p = 0.43) was comparable. Elastography parameters correlated with pain [C|ShS| estimate [β], 0.01 [95% CI: 0.002, 0.02]; p = 0.02); Max|ShS| [β] 0.003 [95% CI: 0.001, 0.005]; p < 0.001)] and disability [C|ShS| [β] 0.02 [95% CI: 0.005, 0.03]; p = 0.009); Max|ShS| [β] 0.003 [95% CI: 0.001, 0.006]; p = 0.002)] scores. Neither C|ShS| (β, 0.13 [-0.27, 0.53]; p = 0.53) nor Max|ShS| (β, -0.02 [-0.10, 0.05]; p = 0.59) changed post-intervention.

Conclusion: Individuals with NSLBP demonstrated elevated TLF shear strain compared to controls, with similar TLF thickness. The shear strain correlated with pain and disability scores, yet a brief massage did not influence shear strain.

Trial Registration: Clinicaltrials.gov, NCT04716101. Registered 14 January 2021, https://clinicaltrials.gov/study/NCT04716101 .

Critical Relevance Statement: Ultrasound shows elevated TLF shear strain in lower back pain sufferers compared to controls. This correlates with symptoms, suggesting a role as a pain generator. Further investigation into its anatomy, mechanical characteristics, and pathophysiology is crucial for better understanding.

Key Points: Structural and mechanical alterations of the TLF may contribute to low back pain. Elevated TLF lateral shear strain was found in patients with NSLBP. A brief standardized massage therapy technique did not influence elastography parameters.