Relationship of kinesiophobia with pain, disability, and lumbar multifidus muscle morphology in chronic mechanical low back pain: an ultrasonographic cross-sectional study

Background: Chronic mechanical low back pain (CMLBP) cannot be explained by biomechanical factors alone; psychosocial factors such as kinesiophobia may also relate to structural changes in trunk-stabilizing muscles. Ultrasonography enables objective assessment of lumbar multifidus morphology (anteroposterior [AP] thickness and cross-sectional area [CSA]). Aims: To investigate the relationship between kinesiophobia and lumbar multifidus morphology among those with CMLBP, and to determine whether this relationship is independent of pain intensity, disability, and demographic/anthropometric factors. Methods: In this cross-sectional study, 100 patients with CMLBP (≥3 months) were assessed using the Visual Analog Scale (VAS), Oswestry Disability Index (ODI), and Tampa Scale of Kinesiophobia (TSK; low <37, high ≥37). Bilateral multifidus AP thickness and CSA were measured ultrasonographically at L4–L5. Group comparisons, correlation, partial correlation, and regression analyses were performed. Results: Mean age was 49.8 ± 12.6 years (68% female); 65% had high kinesiophobia, more frequent among women (76.9% vs. 51.4%, p =.017). The high-TSK group showed higher VAS (6.68 ± 1.98 vs. 5.03 ± 1.71, d = 0.87) and ODI (35.12 ± 15.23 vs. 24.46 ± 11.47, d = 0.76), and smaller multifidus AP thickness and CSA (d = 0.48–0.62). Kinesiophobia scores correlated positively with VAS (r = 0.53) and ODI (r = 0.64), and negatively with multifidus thickness/CSA (r = −0.24 to −0.41). After adjusting for VAS and ODI, the TSK–CSA correlation was markedly attenuated and lost significance (partial r = −0.13 to −0.18, p >.05); after adjusting for age, sex, and BMI, it remained significant (partial r = −0.36 to −0.40, p <.001). Regression confirmed VAS and ODI, but not CSA, as independent predictors of TSK. Conclusions: High kinesiophobia is associated with greater pain, disability, and reduced multifidus morphology among those with CMLBP. However, this morphological association appears largely mediated by pain and disability rather than being independent of them, while remaining unrelated to demographic/anthropometric confounding. These cross-sectional findings support a biopsychosocial framework and warrant longitudinal confirmation.