Posterior Border Distance: An Effective Diagnostic Measurement for Carpal Tunnel Syndrome Using Ultrasonography

Purpose The purpose of this study was to define posterior border distance (PBD), which represents an ultrasonographic diagnosing method of carpal tunnel syndrome (CTS), and to determine the reliability of PBD in comparison with electromyography (EMG) results. Methods Thirty-three patients (mean age: 51.8 ± 9.5 years; 27 females and six males) with CTS were included in this study. Ultrasonography (US) and EMG were performed under blinded conditions. PBD was evaluated by measuring the length of the perpendicular line between the posterior border of the median nerve and the line between the hook of the hamate and trapezoid tubercle. The cross-sectional area, anteroposterior (AP), and transverse diameter of the median nerve were measured. Control US was performed in 20 patients who were available at the first year postoperative follow-up and the results compared with preoperative US values. Correlation analyzes were performed to determine the relationship between electrodiagnostic results and ultrasonographic measurements. Results According to the results of preoperative and postoperative first-year US, there were statistically significant differences in the results of PBD (preoperative: 3.309±1.7472 mm, postoperative: 2.290±0.7867 mm p: 0.013) and AP diameter of the median nerve (preoperative: 3.012±0.7865 mm, postoperative: 2.680±0,5578 mm p: 0.017). There was no statistically significant difference in transverse diameter (preoperative: 6.585±1.9505 mm, postoperative: 6.955±2.2128 mm) and cross-sectional area (preoperative: 14.33±6.513 mm(2), postoperative: 11.20±5.830 mm(2)) results (p>0.05). The cut-off value of PBD was ≥3.6 mm, it yielded 81.48% specificity and 83.33% sensitivity in the diagnosis of CTS. PBD was correlated with motor and sensory latency, anteromedial, and transverse diameter of the median nerve (p<0.05). There was no correlation between EMG values and the results of the cross-sectional area, transverse diameter, and AP diameter of the median nerve (p>0.05). Conclusion PBD is suggested as a reliable ultrasonographic measurement method for the diagnosis of CTS.