Objectives: The contributions of the pudendal and levator ani nerves to the innervation of the levator ani muscle (LAM) are disputed. Because of the relatively large size of the nerves in early life, we investigated this issue in human fetuses.
Methods: (Immuno)histochemically stained serial sections of nine human fetuses (9-22 wk of gestation) were investigated. Both the left and right sides of the fetal pelves were studied individually and 3D reconstructions were prepared.
Results: The levator ani nerve innervated the LAM in every pelvis, whereas a contribution of the pudendal nerve to the innervation of the LAM could be demonstrated in only 10 pelvic halves (56%). In 10 halves, we observed a communicating nerve branch between the pudendal and levator ani nerves that pierced the pelvic floor between the LAM and the coccygeus muscle. No sex differences were observed, but the innervation pattern did differ between the left and right side of a pelvis.
Conclusions: The LAM often has a dual somatic innervation with the levator ani nerve as its constant and main neuronal supply.