[Reexamination of the communicating branch between the sural and tibial nerves]

Reexamination of communicating branches between the sural and tibial nerves ventral to the calcanean tendon was carried out on 52 legs of 26 Japanese cadavers which were used for ordinary dissection practices at the Niigata University School of Medicine. Communicating branches were found in 7 out of 52 dissections (13.5% of cases). In three of the 7 specimens, the communicating branch, the sural nerve and the tibial nerve with the deep crural fascia were removed from the legs and demonstrated by a modified Sihler's staining technique. Three types of communicating branches, Y, U and N, were distinguished on the basis of their shapes. In type Y, a medial branch from the sural nerve and a branch from the tibial nerve joined in Y-shape and become one terminal branch. In type U, the both branches formed a loop between the sural and tibial nerves. The type N communicating branch ran obliquely and medially to reach the tibial nerve distally. Only the Y type appeared in 5 specimens. Both the Y and U type and the Y and N types occurred in one specimen each. We assume that the communicating branch of the N type contains motor fibers which are derived from the sural nerve and innervate some plantar muscles, because this type is correspond to the communication type of some animals in which motor fibers have been demonstrated. Therefore, if the sural nerve biopsy is performed to examine a pure sensory nerve, removal of the more distal part of the sural nerve than a diverging point of a communicating branch is recommended. This study also indicated that the modified Sihler's staining technique is useful to examine distributions of cadaveric peripheral nerves after medical students' dissection course.