Nerve to internal obturator and superior gemellus
The nerve to obturator internus and superior gemellus is formed from the anterior (ventral) divisions of the L5, S1 and S2 nerve roots of the sacral plexus. The nerve supplies the obturator internus and superior gemellus muscles as well as the fascia of the lateral side wall of the ischioanal fossa.
The nerve to obturator internus arises from the anterior divisions of the sacral plexus. It is formed from the L5-S2 nerve roots and exits the pelvis via the greater sciatic foramen inferior to the piriformis muscle and typically between the posterior cutaneous nerve of the thigh and the pudendal nerve.
After supplying a small branch to the gemellus superior muscle the nerve then travels laterally, loops around the ischial spine and passes through the lesser sciatic foramen to reenter the pelvis. The nerve innervates the obturator internus muscle from the medial surface of the muscle in the perineum.
It has been noted in cadaveric studies that the nerve to quadratus femoris and obturator internus frequently arose from a common root and communication between these two nerves have been frequently observed. Various branching patterns to the gemelli have also been observed. The superior gemellus has been demonstrated to receive innervation from branches of the nerve to quadratus femoris as well as twigs from the communication of these two nerves.