Transverse carpal ligament thickness on wrist MRI in carpal tunnel syndrome: a retrospective case–control study

Abstract Carpal tunnel syndrome (CTS) is associated with structural alterations of the median nerve and surrounding components of the carpal tunnel; however, quantitative assessment of the transverse carpal ligament (TCL) remains limited. This exploratory retrospective case-control study evaluated transverse carpal ligament thickness (TCLT) on wrist magnetic resonance imaging (MRI) in patients with CTS and controls. The analysis included 20 clinically classified CTS cases and 20 controls. TCLT was measured on axial T1-weighted images at the hook-of-hamate level, and measurement reproducibility and within-sample discrimination were assessed. Mean TCLT was greater in the CTS group than in the control group (1.24 ± 0.17 mm vs. 0.81 ± 0.16 mm), with a mean difference of 0.43 mm (95% CI, 0.32–0.54; p < 0.001) and a large standardized effect size (Hedges’ g = 2.55). Intra-observer and inter-observer intraclass correlation coefficients were 0.92 (95% CI, 0.86–0.96) and 0.88 (95% CI, 0.80–0.93), respectively. Receiver operating characteristic analysis yielded an area under the curve of 0.97 (95% CI, 0.94–1.00). An internally derived threshold of 1.01 mm yielded a sensitivity of 90.0% (95% CI, 68.3–98.8%) and a specificity of 90.0% (95% CI, 68.3–98.8%) within the present sample. TCLT was greater in selected CTS cases than in controls and showed strong within-sample discrimination. However, given the small retrospective two-gate case-control design and absence of independent validation, these findings should be considered exploratory. The internally derived threshold should not be interpreted as a clinically validated diagnostic cut-off and requires evaluation in larger, independent cohorts using standardized imaging and reference-standard procedures.