Effect of bifid median nerve anomaly on development of carpal tunnel syndrome

Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy. Various causes are reported in CTS etiology. Bifid median nerve (BMN), which is a median nerve anomaly, is one of these conditions leading to CTS. It is considered that BMN would increase the chance of neural entrapment by occupying a larger space in the carpal tunnel. In this study, our goal is to determine whether there is a difference of BMN prevalence in CTS patients compare to healthy population as well as to clarify the influence of BMN on development of CTS. 267 hands of 138 CTS patients and 318 hands of 159 healthy volunteers were evaluated. Demographic features, results from Boston Carpal Tunnel Questionnaire (BCTQ) and visual analog scale (VAS) were recorded for all subjects. Electromyography (EMG) and for BMN evaluation, ultrasonography (USG) were performed. In EMG, median and ulnar nerve conduction studies and if necessary, needle EMG were applied. In USG, entire forearm were screened from volar aspect and results were recorded as "BMN" and "no-BMN". In addition, transverse sectional area (TSA) of all median nerves were measured. Results from patient and control groups were compared. Moreover, patients were analyzed in 6 subgroups, divided according to the CTS severity classification of Padua et. al. Besides, results from BMN and no-BMN groups were compared. Prevalence of BMN was found as 11.6% in 267 hands of patients and 11.0% in 318 hands of healthy population and there was no statistically significant difference between the two groups (p=0.82). When patients were divided into 6 subgroups according to CTS severity, BMS was most frequent in extreme, early and severe CTS groups, respectively. Also there was no difference in BCTQ or VAS scores between BMN and no-BMN groups. Also no correlation was found between BMS and TKA (r=0.083). In conclusion, the prevalence of BMS in patients with CTS does not differ from the prevalence in healthy individuals and the results of this study indicate that BMS is not an independent factor affecting the development of CTS.