The pelvic floor is a very complex area with interrelated myofascial-skeletal, neurovascular and visceral structures and their interactions. The musculoskeletal complex of the pelvic floor itself has long been considered one of the most complex systems of the body, and anatomical and physiological knowledge of these structures continues to evolve. The pelvic floor, classically divided into three compartments, anterior, middle, and posterior, should be considered as a single functional unit: If a defect occurs in one of the three compartments, it may have different effects on the others. For this reason, a multi- or interdisciplinary approach is required when treating patients, involving clinicians or physicians from different specialties, usually physical therapists, nurses, midwives, and physicians. However, other professionals such as fitness instructors and personal trainers can also play a role in the education, health promotion and prevention of pelvic floor dysfunction. The pelvic floor muscles play a very important role in holding urine during physical exertion or increased intra-abdominal pressure: first, by supporting the pelvic organs and restricting the downward movement of the bladder neck. Second, by compressing the urethra distally so that the pressure in the urethra increases before and during exertion, preventing urine leakage.
What is new from the research? (1)
1. Sexual dimorphism of the levator ani muscle (LAM)
That is, the difference in the structure of this muscle in men and women. Typically, this muscle is described as funnel-shaped and attaches to the pubic bone, internal venous muscles, sciatic spines and caudal muscles of the back. It is said to be better developed in women than in men, which is interesting since the muscle mass of women is about 70-75% of that of men. The authors relying on my article attribute this to the fact that the levator ani is more transversely oriented (in the form of a flatter funnel) in women than in men. An important consequence of this flatter funnel in women is the S-shaped configuration of all structures in the posterior small pelvis (rectum and anal canal). The posterior part of the levator ani supports not only the structures just mentioned, but also the uterus and vagina.
2. The puborectalis muscle is part of the anal sphincter complex.
Although the anterior part of the levator ani is well developed, the authors were unable to locate the intermuscular septum of the puborectalis, pubococcygeus, and iliococcygeus muscles as presented in virtually all anatomical textbooks. On the back, however, the orientation of the muscles and the arrangement of their fibers allowed the separation of the puborectalis muscle below and the pubo-visceralis muscle above. The sling-like topography of the puborectalis muscle passing posteriorly through the anal flexure is similar to that often shown in anatomical textbooks. However, in contrast to the classic textbooks (but in agreement with Fritsch and colleagues, who also used a read-across approach), the authors noted that the puborectalis muscle is colocalized with the “deep portion” of the external sphincter (EAS) muscle. Therefore, according to the authors, both names refer to one and the same muscle. The superficial and deep portions of the puborectalis muscle, which correspond to the superficial and deep portions of the external anal sphincter, can be identified in the posterior region where the puborectalis muscle passes after the anorectal junction. Anteriorly, the superficial part of the puborectal/anal sphincter is adjacent to the perineum, whereas the deep part is additionally attached to the pubic bone. Thus, these authors observed two parts of the puborectalis muscle, and Fritsch et al. (Fritsch et al., 2002) considered the puborectalis muscle as a single muscle.
The authors were unable to identify the pubococcygeus and iliococcygeus muscles as adjacent but separate parts of the levator ani, as presented in anatomical textbooks. The authors identified a configuration they called “pubvisceral” because this part of the levator ani slides into the anorectal wall. The term “pubovisceral” was suggested by DeLancey et. al. because of its attachment to the pelvic organs, but in collaboration with Fritsch et al. the authors did not find this attachment. The pubo visceralis muscle had an inner and an outer muscle layer: an inner layer attached to the tendinous body of the perineum and to the fascia surrounding the recto-coccyx muscle on the posterior side. The outer layer consisted of uneven muscle flaps that only partially overlapped the inner layer, and is also attached to the posterior side of the rectococcygeal fascia. The parts of the levator ani muscle, the puborectal and the pubo-visceral (pobovisceral), united at the anterior aspect of the pubis, but differed in their posterior-inferior course, so that the levator ani muscle was considered by the authors to be a biceps. The orientation of the muscle fibers in the anterior LAM is ~ 30 and in the puborectal and pubo visceral muscles lateral to the rectum ~ 45 inclined with respect to the transverse plane, whereas the orientation in the superior pubo-abdominal muscle was predominantly transverse. These numbers agree quite well with estimates from other investigators using MRI.
3. Fibers of the smooth and striated muscles of the medial levator ani muscle.
The fetal pelvic floor examined by the authors showed that the medial posterior smooth muscle cells (from the puborectalis muscle and the sutura recto-coccygea) were closely associated with the inferior rectal plexus, which arises from the inferior hypogastric plexus, i.e., the autonomic sympathetic and parasympathetic nervous systems. These smooth muscle fibers were connected externally to the puborectalis muscle and internally to the rectalis longitudinalis muscle. In addition, in all fetuses examined, the medial anterior smooth muscle cells of the pubo-vaginalis muscle were located in the “bulge” of the levator ani muscle. By delineating the triangular space formed by the vagina, rectum, and levator ani muscle, and in which the inferior hypogastric plexus runs. The smooth muscle cells were connected externally to the pubic and vaginal muscles and internally to the rectum and vagina. They consisted of nerve fibers of the autonomic sympathetic and parasympathetic nervous systems of the inferior hypogastric plexus. These nerve fibers also ran parallel to the smooth muscle bundles that traverse the vaginal wall (2).
What does this mean for physical therapy practice? Read the next article on “The consequences of excessive tension/tonus in the pelvic floor” that can result from overstimulation of the autonomic nervous system.
Martyna Kasper-Jędrzejewska
References:
- Wu Y, Hikspoors JPJM, Mommen G, Dabhoiwala NF, Hu X, Tan LW, i in. Interactive three-dimensional teaching models of the female and male pelvic floor. Clin Anat N Y N. marzec 2020;33(2):275–85.
- Nyangoh Timoh K, Moszkowicz D, Zaitouna M, Lebacle C, Martinovic J, Diallo D, i in. Detailed muscular structure and neural control anatomy of the levator ani muscle: a study based on female human fetuses. Am J Obstet Gynecol. 2018;218(1):121.e1-121.e12.
*It’s not a science about rocket 😉 it’s an expression that means something that is not difficult to understand.
