The Subpubic Angle: Radiological Aspects

Abstract

In view of two recent articles5,6 in the literature in which measurements of a series of subpubic angles are reported, and in which the importance of a narrow subpubic angle as a cause of delay at the pelvic outlet is stressed, it seems pertinent at this time to offer some comments upon this angle as it concerns the radiologist. We have during the past year been making an investigation into radiological pelvimetry, and during our study we have been impressed with the difficulty of measuring this angle accurately and with the paucity of references in the literature to the subject. In many articles the radiological technique is not sufficiently detailed to allow comparison of one series with another, and we have been unable to find any discussion of the possible errors in the methods commonly employed in the measurement of the angle. Criticism is sometimes levelled at radiological pelvimetry as being an inaccurate method, and although we cannot subscribe in general to this opinion, it does appear that there is some justification for it in the case of this particular measurement. This is especially unfortunate, because it appears that the size of the subpubic angle is one of the features of the female pelvis which has a definite obstetrical significance, and accuracy is therefore doubly desirable. The mechanism by which the narrow angle delays or prevents delivery of the head is well described by Nicholson.6