Linea Alba

LINEA ALBA (white line), located along the midline of the abdomen, is a fibrous raphe between the rectus muscles. The skin over the L. a. below the navel is often more heavily pigmented, which is particularly noticeable in women who have given birth; in men, it is often covered with hair. In muscular individuals, when examining the abdominal coverings, a shallow groove is observed from the xiphoid process downward for some distance from the navel; this area corresponds to the wider part of the L. a. The subcutaneous tissue along the L. a., especially below the navel, contains somewhat less fat and is denser than in other parts of the abdominal wall, due to which hemorrhages and abscesses of one half of the abdomen often do not spread to the other half. The fibrous part of the L. a. begins above from the anterior surface of the xiphoid process and below reaches the upper edge of the symphysis (Vol. IV, p. 152, Fig. 3). Slightly below the middle of the L. a. at the level of L_IV, the umbilical ring is located in it. In most cases, the beginning and end of the L. a. appear as a thin cord. At a distance of 2-3 cm downward from the xiphoid process, it gradually widens, and 3-4 cm below the navel it suddenly narrows and, in the form of a narrow tape, extends to the pubic bones, behind which it forms a small triangular expansion. According to Deshin's research, the width of the L. a. at the level of the umbilical ring and 3-5 cm above it varies in men from 0.5 to 4.5 cm, in women from 1 to 7 cm; thus, two extreme types of L. a. are established: narrow and wide; the latter type is more common in women. Kyrimov notes that the width of the L. a. is somewhat greater in those places where it merges with the fibrous raphes of the rectus muscles. According to Napalkov, in addition to the L. a. stretched in width, a soft white line should be distinguished, which is combined with weakness of the abdominal muscles. The L. a. is formed by the crossing of fibrous fibers of the external oblique (m. obliquus ext.), internal oblique (m. obliquus int.), and transverse (m. transversus) abdominal muscles. The tendons of these muscles, forming a sheath for the rectus abdominis muscle (m. rectus abdominis), cross medially from it with the tendons of the same muscles of the opposite side; this crossing forms the white line. Most fibers forming the linea alba are located in an oblique-transverse direction. At the ends of the white line, they are strengthened by longitudinal fibers. The upper longitudinal tendon fibers depart from the anterior surface of the xiphoid process and gradually disappear among the transverse fibers. The lower longitudinal fibers divide into anterior and posterior. The former consist of short bundles that begin from the pubic bone and are located on the anterior surface of the L. a. The posterior ones—more powerful—form the adminiculum lineae albae at its expansion above the symphysis. They begin with a broad base on the upper edge of the symphysis and pubic bone. Rising behind the white line, they gradually disappear among the transverse fibers. At the base of the adminiculum, there is a deep depression that contains a fat lobule; here also branches from the a. and v. epigastrica inf. pass. Deshin distinguishes two extreme types of L. a. according to its structure from the side of the abdominal cavity: 1) fiber bundles on the posterior surface of the L. a. of insignificant thickness are closely adjacent to each other, so that its posterior surface is smooth, and 2) fiber bundles of the posterior part of the L. a. are thicker, do not closely adjoin each other, and in places between them there are slit-like gaps. In the latter case, the posterior surface of the L. a. is covered with protrusions and depressions, which is especially common at the junction of the L. a. with the fibrous raphes of the rectus muscles. These depressions, gradually increasing, can turn into pockets that pass obliquely from back to front through the thickness of the L. a.; in them, a peritoneal diverticulum or lobules of preperitoneal fat can protrude, which gives rise to hernias of the L. a.—The white line, occupying a middle position between the powerful broad muscles of the abdomen, represents a weak point of the abdominal press. The muscles possess active resistance to all pathological factors that stretch the abdominal wall and are able to contract again when the influence of this factor ceases. The L. a., built from tissue of the tendon type incapable of contraction, is more easily subjected to stretching and, once stretched, remains so. Particularly significant stretching of the L. a. is observed in difficult labor. During pregnancy, the entire abdominal wall, especially the L. a., stretches. During intensified contractions of the abdominal muscles during labor pains, the L. a. stretches even more. After the expulsion of the fetus, the stretched abdominal muscles, after some time, contract almost to normal, but the L. a. remains as a stretched membrane. When attempting to sit from a lying position and when standing in the area of such a stretched L. a., a bulging appears between the tensing rectus muscles of the abdomen; this is called diastasis of the rectus muscles.