Very little is known as to its cause, though the consensus of opinion—if any consensus can be said to exist in face of the existing divergent views—appears rather to indicate that it follows falls in awkward positions, sudden efforts, severe prolonged exertion, or tympanites.
In pregnant cows the uterus assumes the appearance of a pendulous organ the body and horns of which constitute the bob of the pendulum, whilst the ligaments represent the cords by which it is suspended. The fixed points are formed by the insertions of the two ligaments in the neighbourhood of the two external iliac angles.
The uterus, however, is also steadied in position by the vagina and by the cellular tissue surrounding it; in fact, in non-pregnant animals it can scarcely be regarded as pendulous, but rather as freely floating and readily yielding to the movements of the surrounding organs.
As soon as the uterus is occupied by a fœtus, however, the conditions become changed. In consequence of the increased weight of its contents the uterus exerts a pull on the broad ligaments and sinks lower in the abdominal cavity. The vagina and the surrounding connective tissue are rendered tense to a degree depending on the increasing weight of the calf. The uterus then more closely resembles a pendulum, the bob being represented by the fœtus and its envelopes. The suspensory apparatus can be divided into three parts, viz., the two broad ligaments and the tissue connecting the uterus to the vagina.
The pull on the vagina increases greatly as soon as the gravid uterus is twisted either to the right or left, for, torsion being attended with more or less extensive displacement towards the lower abdominal wall, the tension on the vagina must become more marked.
Considering now how the spiral folds and the constrictions which are of such importance in diagnosis are formed, we find that both structures, viz., the wall of the uterus and the ligaments, are implicated, though to different degrees. Whilst the spiral folds are more particularly formed by the wall of the uterus, the broad ligaments are chiefly responsible for the constrictions, though to some extent the spiral folds also contribute to their production. The spiral folds of the body of the uterus are formed solely by twisting of its own walls. This can easily be shown by taking any tubular organ whose walls are not too rigid, and twisting it round its horizontal axis.
The broad ligaments contribute less to the formation of the spiral folds, though they play a more important part in producing constrictions and thus in compressing the wall of the uterus.
The symptoms are ill-defined. Sometimes there is difficulty in micturition, but as a rule little evidence exists of any abnormal condition until the advent of labour pains. The first pains, which are usually feeble and separated by rather long intervals, are succeeded by colic. The succeeding efforts steadily become more violent and frequent, but the “water-bag” fails to appear, and in a period varying between twelve and forty-eight hours the pains subside. Rumination is at first suspended, the pulse and respiration are accelerated, and the surface temperature is irregular.
If treatment is not undertaken similar symptoms, but of exaggerated intensity, may again appear in from one to six days. Failing relief death always follows after a varying interval.
The diagnosis is not difficult, provided the maternal passages be examined. On passing a carefully lubricated hand into the vagina the operator discovers, at a varying distance from the os uteri, signs of collapse and twisting of the canal. In cases of quarter twist it is often possible, by rotating the hand so as to follow the spiral folding of the vagina, to introduce the fingers as far as the os uteri; but in half or complete rotation only one or two fingers can be passed so far, or it may be altogether impossible to reach the os.