The Urethral Rhabdosphincter, Levator Ani Muscle, and Perineal Membrane: A Review
Figure 6
Diagram of interface tissue configurations between the rhabdosphincter and levator ani. In panels (a) and (b), muscle fibers of the levator ani directing inferomedially are suitable for upward traction of the rhabdosphincter area, whereas in panels (c) and (d), the fiber directions of the oblique muscle are not suitable for such traction. In panels (a) and (c), the fibrous tissues or fasciae connecting between the levator ani and rhabdosphincter are arranged in series along the axis from the levator to the urethra, whereas in panels (b) and (d), the fasciae along or surrounding the levator and/or the rhabdosphincter area are not suitable for force transduction but for sliding between these two muscles. The morphology shown in panel (a), being similar to the configuration between a skeletal muscle and bone when the connecting fibrous tissues are formed by collagenous fibers, is most suitable for upward traction. The levator and anorectum exhibit this type of morphology, but the connecting tissues are composed of elastic fibers and smooth muscle. The morphology shown in panel (b) is similar to that between the levator ani and external anal sphincter. Panel (c) displays the actual morphology including the levator ani and rhabdosphincter because the fibers of the levator ani muscle are directed to the anorectum, external anal sphincter, and anococcygeal ligament. However, the connecting fibrous tissues contain abundant elastic fibers and smooth muscle. Panel (d) corresponds to the configuration between the levator and vagina that allows mutual sliding.
