Moderate carpal tunnel syndrome: Factors associated with long-term surgery risk after corticosteroid injection

Corticosteroid injection is commonly used for moderate carpal tunnel syndrome (CTS), but factors associated with subsequent surgery remain unclear. This study evaluated baseline clinical, electrophysiological, and ultrasonographic factors associated with long-term surgery risk. This retrospective cohort included 73 of 84 participants with electrodiagnostically moderate CTS from a randomized trial comparing ultrasound-guided and landmark-guided injections. All received a single corticosteroid injection at baseline. Carpal tunnel release was ascertained through structured telephone interviews, with dates verified in national records for 16 of 17 events. Time to surgery was analyzed using Kaplan-Meier estimates and separate two-predictor Cox models. During a median follow-up of 54.7 months, 17 patients (23.3%) underwent surgery. Estimated 48-month surgery-free survival was 79.5%, with a 95% confidence interval (CI) of 68.3-87.1%. Higher baseline visual analog scale pain scores during activity and summed Boston Carpal Tunnel Questionnaire symptom severity scores were associated with surgery in separate adjusted models: hazard ratio (HR) per point 1.51 (95% CI, 1.14-2.00) and HR 1.11 (95% CI, 1.04-1.17), respectively. Longer motor distal latency (MDL) was associated with surgery in both models (HR per millisecond 1.90, 95% CI, 1.05-3.43; and 2.30, 95% CI, 1.24-4.29, respectively). Statistical support weakened with ridge penalization, particularly for MDL. No associations were detected for ultrasonographic measures or injection technique. Greater baseline symptom burden and prolonged MDL were associated with subsequent surgery, but these exploratory findings require validation in larger prospective cohorts before informing treatment selection.