Ossification of the pubic bones at birth.

Abstract

The primary ossification center for the pubic bone usually appears in the superior ramus between the fourth and sixth fetal lunar months (1, 3, 5, 10). It was detected roentgenographically in all fetuses of 340 mm. length (full term) in the series of 640 specimens reported by Francis (3). Obata (7) and Rambaud and Renault (8) described the early center as bean-shaped and usually situated near the margin of the obturator foramen. One gains the impression from the literature that the pubic cartilage is progressively ossified evenly in a single mass (Fig. 1), until the entire pubic bone is mineralized and becomes fused with the ilium above and the ischium below. Hess (5), however, describes a single instance in which two ossification centers were found in one pubic bone, early. In a study of roentgenograms of the pelves of 1,286 randomly selected newborn infants, we have found a variety of patterns of ossification of the pubic bone, with considerable differences in shape and size. We have arbitrarily classified the primary pubic ossification center at birth in three types according to its shape and extent (Fig. 2). In Type A, a single bony mass is limited to the superior ramus. Ossification does not extend as far mediad as the junction of the superior and inferior rami, so that the medial end of the ossification center is not enlarged. In Type B, a single bony mass, shaped like a dumbbell, produces an opaque strip in the superior ramus with globular expansions laterally in the body of the pubis and medially at the junction of the horizontal and descending rami. Ossification does not extend into the descending ramus. The Type C ossification center is shaped like a hook, owing to the extension of ossification beyond the junction of the rami into the descending ramus. A fourth type, Type D (Table I), includes all cases in which there are two or more ossification centers in one or both pubic bones. The demarcation between the first three types is not absolute; one type gradually merges into the next. In one premature infant there was no mineralization of the ossification center. In some cases ossification was more advanced on one side. The prevalence of the four types is shown in Table 1. As would be expected, pubic ossification is least advanced in premature infants. This is demonstrated by the significantly larger percentage of Type A (14 per cent) and smaller percentage of Type C (23 per cent) in premature, as compared to full-term infants (8 percent of Type A, 38 per cent of Type C) (P= 2.8 and 0.5 respectively). Ossification is considerably more advanced in females than in males (Table II). The only significant racial difference was a higher percentage of Type C in white males (37 per cent) as compared to Negro males (27 per cent) (P = 1.6). Continuation studies, not included in this report, showed that ossification of the pubic bone was least advanced at one year in those infants who had exhibited the most primitive ossification at birth.