The anatomy of the recurrent branch of the median nerve.

One hundred one fresh-frozen cadavers were dissected under loupe magnification to spatially define the origin of the recurrent branch of the median nerve and to define its course with respect to the distal edge of the transverse carpal ligament (TCL). The spatial orientation, number, and course of the recurrent branch was carefully determined. Calipers were used to measure the distance between the recurrent branch and the TCL. Histologic analysis of the fascia surrounding the recurrent nerve was performed. The recurrent branch of the median nerve was classified into 3 types. Type I passed through the TCL; it is rare, occurring in 7% of the specimens. Type II nerves (74%) passed distal to the TCL through separate obliquely oriented fascia that originated on the TCL and inserted on the undersurface of the palmar aponeurosis. Type 111 (19%) passed distal to the TCL, but did not pass through the obliquely oriented fascia. The distance from the distal edge of the TCL was significantly different between the 3 types. Ninety-nine percent of recurrent branches originated either from the central portion of the median nerve or just radial to it. There were no ulnar origins. Four cadavers (4%) had more than 1 recurrent branch. The variability in the literature on the anatomy of the recurrent branch can be accounted for by failure to properly identify the TCL as being separate from the obliquely oriented fascia distal to the TCL through which the nerve frequently penetrates. Histologic analysis confirmed a difference between the TCL and these oblique fibers that can surround the recurrent nerve. This study concludes that the transligamentous branch (type I) is uncommon and the reported high incidence of branches passing through the TCL can be explained by mistakenly combining recurrent nerve types I and II.