PRESENTATION OF THE TRUNK.—SPONTANEOUS TION.—SPONTANEOUS VERSION.
In each of these presentations, the foetal head may be on the right or left side, thus: 1st. Right shoulder: Head to the right—Cephalo-iliac right of the right shoulder; Head to the left—Cephalo-iliac left of the right shoulder. 2d. Left shoulder: Head to the right—Cephalo-iliac right of the left shoulder; Head to the left—Cephalo-iliac left of the left shoulder.
There are, therefore, two shoulder presentations, but only two positions for each shoulder, for the anterior, transverse or posterior varieties are here of no importance. But the varieties of presentation are more note worthy. That shoulder, namely, which is the distinguishing point of the presentation, may be relatively distant from the centre of the pelvis, and thus, although it is still the lateral plane of the fcetus, the trunk, which presents, it is not properly speaking the shoulder, but a part dependent upon it, the elbow, which is the most accessible part. We are, there fore, dealing with a variety of shoulder presentations, and for this reason we have, contrary to some authors, taken the head instead of the acro mion as the distinguishing point; otherwise this is a matter of little con sequence, and a glance at the following table will be sufficiently convincing.
The lateral plane of the foetus may present in one of the following ways: Usually, in presentations of the trunk, the hand and the arm prolapse at a certain time into the vagina (Fig. 226), the same hand protrudes beyond the genitals; but this does not constitute a variety of the presen tation. It is a consequence the presentation which, as we shall see, may be utilized in arriving at a correct diagnosis.
Although rarer than pelvic presentations, those of the shoulder are more frequent than face presentations.
Depaul gives 189 among 16,233 cases of labor; P. Dubois gives 13 among 2,022; Pina,rd gives 806 among 100,000.
As to the relative frequency, the researches of Mme. Lachapelle show that the right shoulder presents slightly more often than the left; and that the dorso-anterior positions of the foetus are somewhat more frequent than dorso-posterior positions, in other words, that of the left shoulder and C.I.L. of the right shoulder are the most frequent. The
figures obtained by Depaul confirm the above with reference to the pres entation. Among his 189 shoulder presentations we find: Right shoulder 75 times; Left shoulder 69.
But his investigations do not agree with those of Mme. Lachapelle in regard to the frequency of dorso-anterior positions; for, taking right and left shoulder together, he found 67 cephalo-iliac left dorso-anterior, to 77 cephalo-iliac right dorso-posterior positio The causes of presentations of the trunk (transverse presentations) are those which prevent tho accommodation of the foetus or determine its abnormal mobility, such as some special conformations of tho uterus, smallness of the foetus, premature delivery, hydramnios, foetal tions, maceration of the foetus, faulty insertion of the placenta, multipar ity, laxity of the abdominal walls (according to Pinard, defective tonicity of the uterine wall), but above all, twin pregnancy and contractions of the pelvis; it is evident that the latter are the two causes which are most likely to prevent the normal accommodation of the foetus. Polaillon re lates a case of shoulder presentation in a malformed uterus, uterus septus.
The diagnosis of shoulder presentations comprises three principal points: 1st. Recognition of the shoulder..
2d. Recognition that it is the right or left shoulder.
3d. Recognition that the back is anterior or posterior; that the head is on the right or left side.
Before Labor.
Palpation alone can recognize the shoulder. Indeed, auscultation (although Depaul maintains that in these cases the loudest heart-sounds are heard below or at the level of the line dividing the uterus into two equal parts, but that the sounds diminish in the horizontal, not the ver tical direction) is very apt to be misleading; and the touch ascertains merely that the presenting part is high up above the superior strait and inaccessible to the finger. We convince ourselves, therefore, only of the fact that the excavation is empty, a sign which is common to pelvic and face presentations.