Shear wave elastography assessment of lumbar multifidus muscle elasticity and its correlation with clinical function in patients with lumbar disc herniation

Abstract Background Lumbar disc herniation (LDH) is a common degenerative spinal disease causing low back and leg pain, and dysfunction of the lumbar multifidus muscle is closely associated with its pathogenesis. Current research primarily focuses on muscle strength and morphological assessments, with limited studies quantifying the elastic properties of the lumbar multifidus muscle and their correlation with clinical symptoms and function. Objective To investigate the characteristics of lumbar multifidus muscle elasticity in LDH patients using shear wave elastography (SWE) and analyze its correlation with pain intensity, functional impairment, and LDH classification, thereby providing a basis for clinical evaluation and precision rehabilitation. Methods Thirty-two clinically diagnosed LDH patients (LDH group) and 33 healthy volunteers without low back pain (control group) were enrolled. SWE was used to measure the elastic modulus of the lumbar multifidus muscle in both resting and contracted states. Pain intensity was assessed using the Visual Analog Scale (VAS), lumbar function was evaluated with the Oswestry Disability Index (ODI), and the Macnab classification was obtained from imaging. Differences in the elastic modulus between the two groups were compared, and correlations between the elastic modulus and VAS score, ODI score, and Macnab classification were analyzed in the LDH group. Disc morphology classification was based on the Macnab framework, with the four categories (bulging, protrusion, extrusion, and sequestration) defined operationally according to the NASS/ASSR/ASNR lumbar disc nomenclature [16]. Results Resting-state lumbar multifidus muscle thickness was significantly lower in the LDH group than in the control group (1.03 ± 0.28 cm vs. 1.16 ± 0.23 cm, t=-2.048, P = 0.045), as was contracted-state thickness (1.43 ± 0.39 cm vs. 1.62 ± 0.29 cm, t=-2.239, P = 0.029). Because the elastic modulus data were non-normally distributed, they are reported as median (interquartile range): resting-state elastic modulus was significantly higher in the LDH group (3.10 [2.90–3.32] kPa vs. 2.72 [2.57–3.25] kPa, U = 712.0, P = 0.016), whereas contracted-state elastic modulus did not differ significantly between groups (4.75 [4.19–5.78] kPa vs. 6.29 [3.78–7.83] kPa, U = 412.0, P = 0.130). In the LDH group, resting-state elastic modulus was strongly positively correlated with VAS scores (rs = 0.888, P < 0.001, 95% CI: 0.781–0.944), moderately positively correlated with ODI scores (rs = 0.742, P < 0.001, 95% CI: 0.531–0.867), and not significantly correlated with Macnab classification (rs = 0.014, P = 0.939, 95% CI: -0.336 to 0.361). Conclusions LDH patients exhibit characteristic morphological and elastic differences in the lumbar multifidus muscle, namely reduced muscle thickness and elevated resting-state stiffness; resting-state elastic modulus is closely associated with pain severity and lumbar dysfunction, but not with the Macnab imaging classification of disc herniation. Given the cross-sectional design and the absence of electromyographic confirmation, these findings do not establish whether elevated resting stiffness reflects increased muscle activation or passive tissue changes, and no causal or therapeutic conclusions can be drawn. SWE can quantitatively assess lumbar multifidus muscle elasticity, providing preliminary objective evidence that may inform clinical functional assessment and mechanistic understanding of LDH; further longitudinal and interventional research is needed to establish its diagnostic accuracy, prognostic value, and treatment responsiveness.