Bifid median nerve as an anatomical risk factor for carpal tunnel syndrome: A meta-analysis.

As the median nerve enters the carpal tunnel, it is a single nerve that soon bifurcates into lateral and medial branches into the hand. If the bifurcation is proximal to the carpel tunnel, a bifid median nerve (BMN) results. Carpal tunnel syndrome is often associated with a BMN with or without a persistent median artery. Individual keywords and MeSH phrases were searched in the Google Scholar, SCOPUS, and PubMed databases. Full texts were then collected and assessed for suitability. The prevalence of BMN at the wrist joint in normal and carpal tunnel syndrome wrists (precanal part) and the mean difference between groups were recorded. Only human data were used to test the findings. The pooled odds ratio (with minimal heterogeneity) was 1.50 [1.17-1.93, 95% CI]. The BMN cross-sectional area (CSA) was significantly greater than that of a solitary median nerve in normal wrists. The mean difference in CSA between the two was 1.50 mm 2 [0.56-2.45 mm 2 , 95% CI] without heterogeneity (i 2  = 0). Sex and laterality distributions scarcely differed between the two types of wrists. Owing to the insufficiency of data, the relationships with mean height and weight were not examined. There was a 50% greater incidence of bifid median nerves in carpal tunnel syndrome patients than in normal subjects. A bifid median nerve increases the mean CSA at the wrist joint by 1.5 mm 2 . These findings indicate that the bifid median nerve is an anatomical risk factor for carpal tunnel syndrome.