Ultrasonographic Changes in Median Nerve Cross-Sectional Area After Endoscopic Carpal Tunnel Release in Patients with Early Symptomatic Improvement: A Retrospective Cohort Study

Background/Objectives: Median nerve cross-sectional area (CSA) is an ultrasonographic marker of nerve enlargement in carpal tunnel syndrome, but postoperative changes have been inconsistent. We evaluated 3-month CSA changes after endoscopic carpal tunnel release (ECTR) in patients selected for marked early symptomatic improvement and explored associated factors. Methods: We retrospectively analyzed 43 patients who underwent ECTR and had preoperative and 3-month ultrasonography and Numeric Rating Scale (NRS) data. Changes in CSA and NRS were assessed using the paired t-test and Wilcoxon signed-rank test, respectively. Spearman correlations evaluated associations of CSA reduction with preoperative CSA, symptom duration, electrodiagnostic severity, age, and NRS improvement. Bonferroni correction was applied to the four prespecified candidate correlates other than NRS improvement. Results: CSA decreased from 17.4 ± 5.0 mm2 preoperatively to 14.8 ± 4.4 mm2 at 3 months (mean reduction, 2.65 mm2; 95% confidence interval, 1.73–3.58 mm2; p < 0.001). However, recorded CSA remained unchanged or increased in 9 patients (20.9%). NRS scores (median [interquartile range]) decreased from 6 [5–7] to 3 [2–3]. Neither absolute nor percentage CSA reduction showed a clear association with NRS improvement (ρ = 0.10–0.14; both p ≥ 0.36). Among the four prespecified correlates, only preoperative CSA met the Bonferroni-adjusted threshold, an association susceptible to mathematical coupling. Conclusions: In this early-improvement cohort, CSA decreased overall but did not clearly parallel NRS improvement. The small sample and restricted outcome range limit the ability to exclude an association. Postoperative ultrasonographic findings should be interpreted alongside patient-reported symptoms.