The Symphysis Pubis
Class. - False Synchondrosis. The bones entering into this joint are the pubic portions of the hip-bones. This joint is shorter and broader in the female than in the male. The ligaments, which completely surround the articulation, are:
- Interpubic cartilage.
The superior ligament is a well-marked stratum of yellowish fibers which extends lateralward along the crest of the pubis on each side, blending in the middle line with the interosseous cartilage.
It is continuous in front with the deep traverse fibers of the anterior ligament, and behind with the posterior ligament. It gives origin to the rectus abdominis tendon.
The posterior ligament is slight, and, excepting above and below, consists of little more than thickened periosteum.
Near the upper part is a band of strong fibers, reaching the whole width of the pubic bones, and continuous with the thickened periosteal fibers along the terminal line. Below, many of the upper and superficial fibers of the arcuate ligament ascend over the back of the joint, and interlace across the median line with fibers from the opposite side nearly as high as the middle of the symphysis.
The anterior ligament is thick and strong, and is closely connected with the fascial covering of the muscles arising from the body of the pubis. It consists of several strata of thick, decussating fibers of different degrees of obliquity, the superficial being the most oblique, and extending lowest over the joint.
The most superficial descending fibers extend from the upper border of the pubis, cross others from the opposite side about the middle of the symphysis, and are attached to the ramus of the opposite bone. The most superficial ascending fibers come from the arcuate ligament, arch upward,"and decussate with other fibers across the middle line, and are lost on the opposite side beneath the descending set. There is another deeper set of descending fibers which arise below the angle, but do not descend so far as the superficial; and a deeper set of ascending, which decussate, and reach higher than the superficial set, and are connected with the arcuate ligament. Some few transverse fibers pass from side to side, especially above and below the points of decussation.
The arcuate (inferior or subpubic) ligament is a thick, arch-like band of closety packed fibers which fills up the angle between the pubic rami, and forms a smooth, rounded summit to the pubic arch. On section, it is yellowish in color and three-eighths of an inch (1 cm.) thick in the middle line; it is inseparably connected with the interpubic cartilage.
Both on the front and back aspects of the joint it gives off decussating fibers, which, by their interlacement over the anterior and posterior ligaments of the symphysis, add very materially to its security. In fact, the ligament may be said to split superiorly into two layers, one passing over the front, and the other over the back, of the articulation.
The interpubic fibro -cartilage varies in thickness in different subjects, but is thicker in the female than in the male. It is thicker in front than behind, and projects beyond the edges of the bones, especially posteriorly, blending intimately with the ligaments at its margins. It is sometimes uninterruptedly woven throughout, but at others has an elongated narrow fissure, partially dividing the cartilage into two plates, with a little fluid in the interspace. This is situated toward the upper and posterior aspects, but does not usually reach either; it generally extends about half the length of the cartilage.
When this cavity is large, especially if it reaches or approaches very near to the circumference of the cartilage (which, however, it very rarely does), it is thought by some anatomists that it more nearly resembles a diarthrodial than an amphiarthrodial joint, and it is then classed with the sacro-iliac joint under similar conditions, as 'diarthroamphiarthrosis.' The interosseous cartilage is intimately adherent to the layer of hyaline cartilage which covers the medial surface of each pubic bone; the osseous surface is ridged to give a firmer attachment; and, on forcing the bones apart, it does not frequently split into two plates, but is torn from the bone on one side or the other.
The arterial supply of the interpubic joint is from twigs of the internal pudic, pubic branches of the obturator and epigastric, and ascending branches of the internal circumflex and superficial external pudic.
The nerve-supply has not been satisfactorily made out, but it probably comes, m part, from the internal pudic and in part from the ilio-hypogastric and ilio-inguinal.
The movements amount only to a slight yielding of the cartilage; neither muscular force nor extrinsic forces produce any appreciable movement in the ordinary condition. Occasionally, as the result of child-bearing, the joint becomes unnaturally loose, and then walking and standing are painfully unsteady. It is known that, during pregnancy and parturition, the symphyseal cartilage becomes softer and more vascular, so as to permit the temporary enlargement of the pelvis; but it must be remembered that the fibers of the oblique muscles decussate and thus, during labour, while they force the head of the fetus down, they strengthen the joint by bracing the bones more tightly together.
Relations. - The interpubic joint is in relation above with the linea alba. Behind with the prostate and the anterior border of the bladder. In front with the suspensory ligament of the penis or clitoris and below with the dorsal vein of the penis or clitoris and the upper border of the urogenital trigone (triangular ligament).