A Simple and Practical Thenar-Hypothenar Measurement Approach for Assessing the Severity of Carpal Tunnel Syndrome

Objective: To determine whether the thicknesses of the thenar and hypothenar regions measured at the bedside using a caliper, along with their ratio (thenar/hypothenar; T/H), reflect the clinical and electrophysiological severity of carpal tunnel syndrome (CTS), and whether preoperative T/H asymmetry (Δ(T/H)) predicts postoperative functional recovery. Methods: This prospective case-control study included 50 patients with electrophysiologically confirmed CTS and 50 age- and sex-matched healthy controls. Thenar and hypothenar thicknesses were measured using a standard caliper protocol, and the T/H ratio was calculated. Symptoms and function were assessed using the Boston Symptom Severity Scale and the Functional Status Scale. Electrophysiological severity was classified based on sensory and motor conduction findings. Patients were re-evaluated 3-6 months after surgery. Results: Thenar thickness and the T/H ratio of the operated hand were significantly lower in CTS patients compared to controls (p < 0.001). T/H asymmetry, defined as Δ(T/H) = T/H (non-operated) - T/H (operated), showed significant differences according to motor severity categories (p = 0.002) and sensory severity categories (p = 0.004). Δ(T/H) was positively correlated with functional status (FSS) (Spearman ρ = 0.33; p = 0.018) but was not correlated with symptom severity (SSS) (p = 0.738). Preoperative Δ(T/H) showed a positive correlation with postoperative FSS (Spearman ρ = 0.34; p = 0.015). In a multivariable logistic regression adjusted for diabetes mellitus, age, and BMI, Δ(T/H) remained independently associated with severe motor involvement (adjusted OR = 1.26 per 0.01 increase in Δ(T/H); 95% CI, 1.07-1.49; p = 0.006), while diabetes mellitus was not independently associated (p = 0.674). Conclusion: Caliper-based thenar/hypothenar assessment incorporating contralateral comparison (Δ(T/H)) is a practical bedside adjunct method reflecting electrophysiological severity and functional limitation and may aid in predicting postoperative functional recovery; larger validation studies are needed.