On the Mechanism of Labour in the Common Forms of Contracted Pelvis, with Remarks regarding Diagnosis
Authors: O. Spiegelberg
Journal: BMJ (1873)

THE minor forms of contracted pelvis are much more common than is generally supposed, and they are rarely recognised by the general prac- titioner.Nevertheless, they are frequently the cause of abnormities in labour which are regarded as of independent origin; for example, pre- mature rupture of membranes, prolapsus of funis, irregular presentations and positions.I have, therefore, considered myself justified in taking up the time of the Association with an attempt to throw some light on this difficult subject.The most common forms of narrowed pelvis we have to deal with are- I. 'T he simply flat pelvis [contracted only in the conjugate diameter].2. The generally and uniformly contracted pelvis, pelvis tecztabiliter justo minor.3. The generally contracted flat pelvis, a combination of forms I and 2.Their diagnosis is very easy, although generally represented as very difficult.Leaving aside the signs furnished by inspection, anamnesis, etc., the measurement of the pelvis consists in defining by a conpas -d'Jaisseura.The distance between the anterior superior spines of the ilia- {Sp.Il.] b.The distance between the crests of the ilia-The measurements of the distances between the spines and the crests of the ilia may give one of the three following results.I. Both distances are less than they ought to be, but the relation of one to the other [the distance between the crests being from two to three centimeters longer than that between the spines] remains unchanged.2. The distance between the crests is not, or at most very little, ,diminished, but that between the spines is increased.3. Both distances are diminished, but at the same time their mutual relation is not normal, the distance between the spines being as long as, if not longer than, between the crests.The result No.I denotes an universally and uniformly contracted pelvis.The result No. 2 denotes a pelvis not small, but enlarged in the transverse and contracted in the antero-posterior diameter.The result No. 3 denotes a combination of I and 2; that is, a generally ssmall pelvis with contraction in the antero-posterior diameter.The measurement of the external conjugate is only reliable in cases of great deviation from the normal length.Only when it is found to measure under seventeen centimeters, it may be concluded that there exists a pelvis contracted in the antero-posterior diameter.All the results obtained in the abovementioned ways are corroborated or corrected by the measurement of the diagonal conjugate.This is always done by the hand alone; and, while doing it, search may at the same time be made for other signs of contraction within the pelvic cavity.To estimate the length of the true conjugate [C.v.], you have to subtract from the length of the diagonal conjugateabout one centimeter and a half.But, if in all cases this average of one and a-half be taken, there is risk of often falling into great error; for, as my observations have taught me, the difference may vary from one to three centimeters.How much is to be subtracted in an individual case, will depend principally on three points:a.The depth of the symphysis pubis; b.The direction of the anterior wall or the symphysis in regard to the posterior; c.The height to which the promontory rises above the anterior border of the pelvic brim.The deeper the symphysis, the more vertically it is directed, the more elevated the promontory-the greater is the difference between the diagonal and the true conjugate, the more you have to subtract from the former to find the length of the latter.I need not mention that these relations may exist in different combinations.