THREE seems to be a general misconception concerning the anatomical structure and functions of the normal levator ani, and little appreciation of the influence it may exert on child-birth, and of the accidents to which it is liable.
Being generally disregarded when normal in character, it naturally follows that it is often overlooked when abnormally developed, and the evil consequences resulting from its injury not generally understood.
Enclosing, as it so nearly does, supplemented by the coccyges, the pelvic outlet, it has been called “the diaphragm of the pelvis”.
In most cases it is so thin as to be nearly membranous, its fibres being arranged in flat bundles, loosely held together, with here and there spaces filled with fat and connective tissue. This peculiarity of structure adapts it most favorably to bear the strain and distension incident to child-birth.
The levator ani has its origin in part from the bones and in part from the fascia of the pelvis. Of those portions having a bony origin the larger and more important is that coming form the horizontal ramus of the pubes. This portion, moreover, most interests us as obstetricians.
The anterior edges of this muscle do not meet at the symphysis, but are separated by a space of about an inch. The portion arising from the pubes is, it its point of origin, about one and one-half inches wide, and its insertion is about one and one-fourth inches below the upper of the ramus.
This bundle of fibres is much thicker than the rest of the levator, and its edges are so thickened and rounded as to itself resemble, to the touch, two independent bundles of fibres. In some cases it becomes so hypertrophied as to give rise to severe vaginismus and dystocia. Following the origin backward from the pubic ramus it is found to arise form a crescentic-shaped line of fascia extending to the ischial spine, whence arises that smaller portion which has a bony origin. The portion arising from this curved line of fascial origin is strengthened by the pelvic fasciae, the tendinous fibres of which are flattened and spread out upon both its upper and under surfaces.
The course of this muscle is downward and backward, and, except a small bundle of fibres, extends back of the rectum. That which passes anterior to the rectum is a bundle of fibres only a few lines wide. It has its origin at that point of pubic attachment farthest from the symphysis, and, crossing the larger belly of muscle in a diagonal direction, is lost in the recto- vaginal septum about half an inch from the anus.
While usually in women this portion of the muscle is quite small, in some instances it is markedly strong and hypertrophied, as may be proved by careful recto-vaginal examination. With the exception of this bundle of fibres, that portion arising from the pubes, which as we have said, is the largest, extends as one continuous strip of muscular tissue from its origin on the ramus of one side down alongside the vagina, to which it is attached by strong connective tissue and by an interweaving with some of the longitudinal muscular fibres of the vagina around the back of the rectum to its point of attachment on the ramus of the other side.
Some of its fibres are interwoven with the longitudinal fibres of the rectum, but, as in the walls, of the vagina, they do not lose their identity. This band is intimately connected with the sphincter ani, some fibres crossing or interweaving with some of the sphincter fibres, which are inserted into the dorsal surface of the coccyx. As the muscle spreads out towards the coccyx its handles become flatter and thinner. It huge the concavity of the curve-end of the rectum and supports it from below. The middle portion joints its fellow by aponeurosis at the point of the coccyx. The smallest and posterior portion is fixed by tendinous attachment to the fourth coccygeal vertebra.
The functions of the levator are primarily to aid in defecation. In woman, however, it has other functions. It draws the anus and posterior wall of the vagina towards the symphysis, and during coitus, as a vaginal constrictor, presses the penis firmly against the os tincae.
In strength it varies greatly, it being found strongest in women of strong muscular build, of erotic disposition, with wide pelvis, and in those suffering from painful lesions around the vulva and anus.
By careful experiment the average lifting power has been found to be ten pounds, while in some it is as high as twenty- seven pounds. There are reported instances of tonic spasm of the muscle during copulation so strong as to require anaesthesia for the release of the imprisoned penis.
This abnormal development and increased strength of the levator is not infrequently called upon to compensate for other defects. A woman past eighty years, while ill from other troubles, complained of piles. Much to my surprise I found a complete laceration of the perinaeum. I had known her for fifteen years as a remarkably smart and robust old lady. She had borne several children, and I could not learn that she had ever suffered from uterine trouble or incontinence of faeces.
The womb was certainly then in normal position. The levator was very strong, and so contracted as to draw the anus well forwards towards the symphysis, thus perfectly compensating, as far as support to the vaginal walls and womb were concerned, for the destroyed perinaeum; and what seems more remarkable, had so closed the anus that the loss of the sphincter had caused no inconvenience.
Not long since I examined a patient with perinaeum gone to the sphincter; she had suffered nothing from want of support to the organs above. As in the former case, the strong levator had so drawn the anus forwards as to form a substitute for the perinaeum. Whether a rectal polypus has been a constant whip to keep the levator in a state of contraction cannot be said. Only lapse of time-now that the polypus has been removed-can answer, which it will have a chance to do, since she can see no necessity for having the perinaeum restored.
In ordinary cases its dystotic power, when it is not abnormally strong from hypertrophy, may not seem very great.
Physiological relaxation, paralysis from continued tension and from compression all tend to reduce its opposing power to the minimum. A careful comparison of the levator, reinforced, as it is by firm fasciae, with the diaphragm, will show that its average resisting power is not inconsiderable.
As before stated, however, we not infrequently find the levator greatly strengthened by hypertrophy. This is most marked in the anterior portion that has its origin from the rami of the pubes and exerts the most power in drawing the anus and vagina forward towards the pubes. The hypertrophy may, however, involve the entire muscle or only independent portions of or bands of fibres.
It is claimed that the levator ani usually becomes hypertrophied during pregnancy. Painful lesions in the anus, like piles and fissures-which are so frequent a complication of pregnancy-tend to keep the muscle in a state of active contraction, which is promotive of hypertrophy. This condition of the anus, irritated by the pressure from the approaching part, may set up a tonic contraction of the levator. Not infrequently labor progresses naturally, with promise of a speedy delivery, until the presenting part comes in contact with the floor of the pelvic-in other words, with the levator ani. Pain succeeds pain, each causing the presenting part to press firmly upon the opposing tissues; but in the interval between the pains it recedes to its former position, no advance being made.
The muscles of propulsion, already wearied by long-continued effort, meet a fresh and untried opponent. The naturally stronger yields, through fatigue, to the weaker. The pains lessen in force and frequency. Longer delay places the life of the child in jeopardy, and the hot, dry vagina, quick pulse, wearied yet anxious face of the mother call loudly for her relief. Now, or even before this extreme condition has been reached, the very short forceps (Hale’s) are most useful. Being small, with almost no shank between the blade and handle, they can be easily adjusted and often without the knowledge of the patient.
Then, if just sufficient traction be applied to prevent the presenting head from receding in the intervals between the pains, the levator is kept in a state of continued tension, with such paralyzing effect as to soon cause it to lose its power of resistance, and the delivery is accomplished easily.
If, however, hasty delivery be demanded, anaesthesia should be carried to the surgical degree, in order to produce complete relaxation of the muscle and avoid rupture.
In case the anus be sensitive and painful, from fissures or ulcers, complete anaesthesia is of vital importance; for, as all surgeons know, putting a sensitive anus on stretch will arouse violent reflex muscular action, which can only be overcome by complete anaesthesia. If this precaution be not observed, the levator, being in a state of tonic contraction, delivery will most likely be accomplished with a rupture of the perinaeum and some portion of the levator ani.
