The Role of Musculoskeletal Ultrasound in Detecting Superior Cluneal Nerve Entrapment: Biomechanical Insights in Chronic Low Back Pain—A Pilot Study

<b>Background</b>: Superior cluneal nerve (SCN) entrapment is frequently underrecognized as a contributor to chronic Low Back Pain (cLBP) and gluteal pain. Musculoskeletal ultrasound may reveal surrogate markers indicative of a biomechanical entrapment environment. The primary objective was the prevalence of the ultrasound marker triad (Copeman Nod-ules-CN, thoracolumbar fascia-TLF thickening > 3 mm, and iliac enthesophytes. Secondary objectives included mean TLF thickness and its correlation with numeric pain rating scale (NPRS) and Douleur Neuropathique en 4 questions scores (DN4). <b>Methods</b>: In this single-center, cross-sectional observational pilot study, we enrolled 12 patients with cLBP (>12 weeks) localized to the SCN distribution and a healthy control group (12). Ultrasound measurements included TLF thickness in longitudinal and transverse planes, TLF convexity loss, iliac crest enthesophytes, and CN. Statistical analyses comprised Mann-Whitney U test, Fisher exact test, Spearman rank correlation, and multivariate logistic regression. Significance was set at <i>p</i> < 0.05. <b>Results</b>: The ultrasound marker triad (CN, iliac enthesophytes, and TLF thickening > 3 mm) demonstrated high diagnostic specificity: individually, CN were present in 91.7% of patients vs. 8.3% of controls (<i>p</i> < 0.001), iliac enthesophytes in 58.3% vs. 0% (<i>p</i> = 0.005), TLF thickening > 3 mm in 41.7% of patients vs. 0% of controls (<i>p</i> < 0.001)and TLF convexity loss in 100% vs. 75% (<i>p</i> = 0.03). Mean TLF thickness was significantly greater in patients-3.53 ± 0.46 mm longitudinal and 3.42 ± 0.39 mm transverse-compared with controls (2.61 ± 0.28 mm and 2.50 ± 0.32 mm; both <i>p</i> < 0.001). TLF thickness correlated strongly with NPRS (Spearman rho = 0.825; <i>p</i> = 0.001) but not with DN4. Logistic regression demonstrated that the marker triad accounted for 67% of NPRS variance (R² = 0.67). <b>Conclusions</b>: Ultrasound-detected fascial alterations and enthesopathic changes act as reliable surrogate markers for SCN entrapment and correlate strongly with nociceptive pain severity. The absence of correlation with neuropathic pain scores suggests a predominant fascial-muscular biomechanical mechanism rather than direct nerve damage. Incorporating this non-invasive protocol into clinical practice may enhance diagnostic precision and inform targeted rehabilitative strategies. Future multicenter, prospective studies with larger cohorts are warranted to validate these findings and establish standardized ultrasound criteria.