Causes.—These are predisposing and determining. Most authors ad mit the influence of multiparity. Among 1164 cases of rupture collected by various authorities, 616 occurred in multiparfe. In consequence of child-bearing the uterine walls are softened, fatty degeneration resulting from repeated pregnancies, with consequent weakening of the power of the uterus, prolongation of the labor, and (according to Scanzoni), greater frequency of trunk-presentations.
Duration of Labor.—Simpson's statistics show that when labor extended beyond twenty-four hours, there was one case of rupture in 38, but when it lasted only 6 hours, there was but one case in 2000. Trask found the mean duration of labor in 57 cases of rupture to be 21 hours and 6 min utes.
Contraction of the Pelvis.—Trask noted the presence of contraction in 74 per cent. of 300 cases of rupture. The accident seems to be more common where the contraction is only moderate, as when the narrowing is excessive the cervix is always above the brim of the pelvis, and, as the fcetal part can not engage, there is no chance for compression of the uterus against the bone. Rupture is said to occur more frequently with male infants.
Thinning of the Uterine Min.—This was noted by Trask in 14 out of 49 ruptures; by Wilmart, in 21 out of 100. Softening from metritis, fatty degeneration, malignant disease, etc., is another cause. Cicatrices in the uterine walls, from former wounds, Cfesarean section, etc., have been noted in some cases. Rigidity of the cervix, uterine tumors, etc., may be causes. Hydrocephalus in the fcetus was noted as a cause by Keith in 16 cases out of 64, by Bandl in 2 out of 13, by Kohl in 5 out of 77. Excessive size of the foetus was a cause in 10 out of 63 cases reported • by Kormann. Presentations of the shoulder are especially unfavorable; they were observed 14 times in 84 cases. Unusual development of the fundus uteri, and malformations of the organ have given rise to the ac cident. The immoderate use of ergot is a fruitful cause.
Traumatic ruptures are mostly due to blows and to version. Among 197 cases of traumatic rupture, 71 followed version, 37 the employment of the forceps, 10 cephalotripsy, and 30 other unwise manipulations. Many writers claim that rupture may take place before the membranes are ruptured.
Pathological Anatomy.—Location.—The posterior wall of the inferior segment is the most common locality, and next to this the lateral walls, especially the left. The rupture is usually single, but may be multiple; there may be simply a perforation of the uterine tissue, but more com monly the lesion presents a considerable extent (3 inches and more); sometimes the uterus is almost completely detached from the vagina, or the rent may extend from the inferior segment to the fundus, involving also the cervix, vagina, rectum, or bladder. As a rule the peritoneal layer is not involved, being merely detached by the extravasated blood; rarely the peritoneum is torn, while the other layers are intact. The
foetus may remain in the uterus or escape into the cavity. The rent may be vertical, transverse, or oblique, generally with irregular edges. The blood escapes into the abdominal cavity, and spreads beneath the peritoneum.
Mode of theories have been advanced: according to the first, the uterine contraction is the sole cause of the rupture, while the second refers the accident to obstetric manipulations, and according to the third rupture is due to the compression of the uterine tissues be tween the foetal head and the pelvic wall, thus producing softening and gangrene. According to Bandl's theory the cervix retracts above the foetal head after complete dilatation, this retraction being produced by the combined muscular contraction and the elasticity of the tissue. In primiparte, during the stage of dilatation, there is the greatest develop ment of the uterine force for the purpose of expelling the child. The external muscular layer in contracting both exerts a concentric action on the contents of the uterus, and tends to draw the uterine wall upwards over the foetal ovoid. The concentric pressure then tends to engage the child in the cervix, and it is only when the cervix is greatly distended by the foetal part that the second factor becomes active, that is to say, the elasticity of the cervix, which causes it to retract above the head. When there is no obstacle offered to this ascension of the cervix, there occur in primiparie only those small, insignificant lateral tears which are observed in the portio vaginalis, and which may sometimes be entirely assent. When the relations between the head and the pelvis are not quite normal, delivery is somewhat more difficult, and the lacerations of the cervix are deeper. As a rule the anterior wall of the cervix is, so to speak, imprisoned between the head and the pelvis, at a level more or less ele vated, and the head in descending pushes the cervix downwards and dis tends it at that point which we see appear at the vulva as a bluish or red dish swelling. More extensive tears sometimes take place in this case, especially where small ones existed before, because, as the head is forced downward, and the muscular contraction acts in an upward direction, both forces act upon the cervix, the posterior wall of which is already re tracted over the head, while the anterior is still impacted. Band I has often observed under these circumstances lacerations of the cervix, in- I one-half of the cervix and the internal layers of the same, with out causing the death of the women. These lacerations may also be pro duced when the foetus is extracted after version, especially in cases of con tracted pelvis.