Shearwaveelastographybasedanalysisofchangesinfascialandmusclestiffnessinpatientswithchronicnon-specificlowbackpain

Low back pain is one of the leading causes of disability worldwide, with the vast majority of cases being "non-specific" — meaning no clear structural cause can be identified. When this pain persists for more than three months, it becomes classified as chronic non-specific low back pain (CNLBP). While doctors can see muscle degeneration and fat buildup in imaging studies, these structural changes don't fully explain why patients hurt or how disabled they become. The muscles and fascia (connective tissue) of the lower back have important mechanical properties like stiffness and elasticity that affect how they function, but these properties are invisible on standard imaging like MRI or X-ray.

Researchers have suspected that increased stiffness in the thoracolumbar fascia (TLF), erector spinae (ES), and multifidus (MF) muscles might contribute to pain and disability in CNLBP, but measuring this stiffness objectively has been difficult. Shear wave elastography (SWE) is a newer ultrasound technology that can quantify tissue stiffness without relying on examiner pressure, making it potentially ideal for studying these deep back structures. This study aimed to compare stiffness in these tissues between people with and without CNLBP, and to see if stiffness correlated with how much pain and disability patients experienced.

The researchers recruited 30 patients with CNLBP from a hospital spine surgery outpatient department and 32 healthy volunteers without back pain. All participants were young to middle-aged adults (20–38 years old). The CNLBP patients had persistent low back pain for at least 3 months, with pain located between the lower ribs and the top of the buttocks, and no specific causes like herniated discs, fractures, tumors, or inflammatory diseases. Healthy controls had no history of chronic back pain or spinal disorders.

Using a specialized ultrasound machine in shear wave elastography mode, the researchers measured stiffness (quantified as shear modulus in kilopascals) at two spinal levels: L1–L2 (upper lumbar) and L4–L5 (lower lumbar). At each level, they measured bilaterally (both left and right sides) the thoracolumbar fascia, erector spinae muscle, and multifidus muscle. Participants lay face down with a pillow under their abdomen to flatten the natural curve of the lower back. The examiner carefully positioned the ultrasound probe parallel to muscle fibers to account for the anisotropic nature of muscle tissue, and an assistant froze images when the motion stability index reached optimal levels.

For the CNLBP group, the researchers also recorded pain intensity using the Numeric Rating Scale (NRS, 0–10) and functional disability using the Oswestry Disability Index (ODI, expressed as a percentage). They then used statistical tests to compare stiffness between groups and correlation analyses to examine relationships between stiffness and clinical symptoms, while controlling for age, height, weight, and BMI.

The CNLBP group showed significantly higher stiffness than healthy controls in multiple measurements. At the L4–L5 level, stiffness was significantly increased in all measured structures: bilateral thoracolumbar fascia (left: p=0.014, d=0.64; right: p=0.002, d=0.86), bilateral erector spinae (left: p=0.013, d=0.66; right: p=0.027, d=0.58), and bilateral multifidus (left: p=0.009, d=0.69; right: p=0.002, d=0.85). At the L1–L2 level, significant differences were more limited: the right erector spinae (p=0.026, d=0.59) and left multifidus (p=0.020, η²=0.09) showed higher stiffness in CNLBP patients, but other measurements at this upper level did not reach statistical significance.

The correlation analyses revealed that higher stiffness was associated with greater pain and disability, but primarily at the L4–L5 level and especially in the thoracolumbar fascia. For pain (NRS scores), strong correlations were found with bilateral TLF stiffness at L4–L5 (left: r=0.57, p=0.001; right: r=0.65, p<0.001). Moderate correlations with NRS were seen for ES at L4–5 (left: r=0.42, p=0.022; right: r=0.48, p=0.007) and MF at L4–5 (left: r=0.50, p=0.005; right: r=0.42, p=0.023), as well as left MF at L1–2 (r=0.50, p=0.005).

For disability (ODI scores), strong correlations were again found with bilateral TLF at L4–L5 (left: r=0.60, p<0.001; right: r=0.58, p<0.001). Moderate correlations with ODI included right TLF at L1–2 (r=0.43, p=0.017), right ES at L1–2 (r=0.38, p=0.037), and bilateral MF at both levels (L1–2 left: r=0.46, p=0.011; right: r=0.45, p=0.012; L4–5 left: r=0.44, p=0.015). No significant correlations were found at other measurement sites.

This study provides objective evidence that people with chronic non-specific low back pain have measurably stiffer fascia and muscles in their lower backs compared to pain-free individuals, with the most pronounced changes occurring at the L4–L5 level. The finding that stiffness correlates with both pain intensity and functional disability — particularly in the thoracolumbar fascia — suggests that these tissue mechanical properties may be clinically meaningful contributors to the CNLBP experience.

For clinicians, this research supports the importance of addressing tissue stiffness in CNLBP management. Manual therapies, movement interventions, and other treatments that can modify fascial and muscular stiffness may be particularly relevant. The strong association between TLF stiffness and symptoms also highlights the thoracolumbar fascia as a potential therapeutic target that deserves more attention than it traditionally receives.

For patients, these findings help validate that their pain involves real, measurable changes in tissue properties — not just something "in their heads" or visible only as structural damage on MRI. The non-uniform distribution of stiffness changes (worse at L4–L5 than L1–L2) aligns with clinical understanding that the lower lumbar spine bears more mechanical stress and is more prone to problems.

The study also positions shear wave elastography as a promising tool for objectively assessing CNLBP. Unlike subjective palpation or structural imaging that doesn't show mechanical properties, SWE provides quantitative stiffness measurements that could potentially help diagnose CNLBP, monitor treatment response, and guide personalized rehabilitation. However, the cross-sectional design means we cannot determine whether increased stiffness causes pain, results from pain, or both — longitudinal studies tracking stiffness changes with treatment will be needed to clarify these relationships.