A reappraisal of the anatomy of the levator ani muscle in man.

A study of the attachments of the musculotendinous fibres of the levator ani muscle shows that it is made of two portions: a thick anterior portion which is mostly fleshy and a thin posterior portion which is mostly aponeurotic. The anterior portion consists of two layers: a superficial perineal layer and a deep pelvic layer. Both layers have a common origin from the back of the body of the pubic bone and the anterior part of the tendinous arch. In addition both layers make a U-shaped loop around the recto-anal junction. The posterior fibres of the deep pelvic layer received nerve supply only from the third and fourth sacral nerves. The rest of the muscle was supplied from the sacral nerves as well as the perineal branches of the pudendal nerve. The role of the anterior fibres in reinforcing the sphincters of the anal canal and fixation of the pelvic viscera is stressed. The close anatomical relation between the posterior portion of the muscle and the obturator internus suggests that the latter may play a role in supporting the weak posterior portion of the levator ani, especially during straining positions associated with lateral rotation at both hips.