Thoracolumbar fascia ultrasound and elastography biomarkers in low back pain: a systematic review of associations and responsiveness to intervention.

BACKGROUND AND AIM: Traditional imaging methods often fail to identify the causes of nonspecific low back pain (NSLBP). The thoracolumbar fascia (TLF) has gained attention as a potential target for assessment with Quantitative Ultrasound (QUS). This systematic review examines the relationships between TLF QUS biomarkers (stiffness, shear strain, morphology, and microstructure) and NSLBP and how these biomarkers respond to interventions. METHODS: Adhering to PRISMA 2020 guidelines, searches were conducted in MEDLINE, EMBASE, CENTRAL, and Scopus up to February 2026 for studies evaluating TLF QUS biomarkers in adults with NSLBP. Risk of bias was assessed using RoB 2, ROBINS-I, and NOS. Due to methodological heterogeneity, a narrative synthesis was performed. FINDINGS: Fourteen studies involving approximately 880 participants met the inclusion criteria. In chronic NSLBP, several studies reported greater TLF thickness, altered echogenicity or microstructural texture parameters, and differences in stiffness compared with asymptomatic controls. However, stiffness findings were inconsistent across elastography modalities, with both higher and lower stiffness-related measures reported. Functional mobility findings also varied by clinical population and measurement protocol: studies in acute LBP generally reported reduced deformation, whereas studies in chronic LBP reported either reduced or increased shear strain. Preliminary intervention studies indicated changes in TLF thickness and selected stiffness-related measures following manual interventions, whereas single-session massage did not produce detectable changes in shear strain measures. INTERPRETATION: QUS studies have identified differences in TLF morphology, mechanical properties, mobility, and microstructural texture parameters between some individuals with NSLBP and asymptomatic controls. The direction and magnitude of these differences are not uniform and vary across populations, imaging modalities, and acquisition protocols. The available findings may be consistent with different patterns of fascial mechanical behavior, but the existence of distinct biological or clinically actionable TLF phenotypes remains hypothetical and requires prospective validation. Evidence regarding responsiveness to intervention is preliminary, and the clinical utility of these parameters for diagnosis, treatment selection, or outcome monitoring has not yet been established.