The pubic symphysis is a fibrocartilaginous joint that unites the two pubic bones at the pelvis anteriorly, and is stabilised by surrounding ligaments. Pain in the region of the pubic symphysis, also known as symphyseal pain or symphyseal dysfunction can affect a diverse group of individuals, including women during pregnancy, birth and/or the post-partum period. Pregnancy-related symphyseal pain is relatively common, but the pathogenesis of this problem is poorly understood. Hormonally induced biomechanical changes at the pubic symphysis during pregnancy, is the commonly accepted cause of this condition.
Before interpreting pathology it is important to understand normality. Results of a systematic anatomical review on the adult human pubic symphysis revealed that some morphological aspects of the joint are still unclear, including precise attachment sites of surrounding ligaments and the detailed constitution of the interpubic disc. The last anatomical study of the pubic symphysis dates back to 1986. Hence, a detailed anatomical investigation of the joint using modern, state of the art techniques is needed.
In the initial healthy volunteer study the pubic symphysis was examined using ultrasound in 30 young nulliparous women (mean age 26 years, range 18-35 years). Quantitative data for ultrasonographic anatomical parameters at the pubic symphysis were established, including narrow and wide joint widths, the length and depth of the superior pubic ligament (SPL) and pubic crest length. Further, the inter- and intra-observer reliability for measurements taken by an experienced and inexperienced sonographer were established. Larger ultrasonographic anatomical parameters at the joint, such as wide pubic symphysis width and SPL length, could be measured more reliably than smaller measurements such as narrow joint width and SPL depth. In an accompanying cadaver validation study, of six elderly postmenopausal cadavers (mean age at death 75 years), the accuracy of ultrasonographic measurements at the pubic symphysis was examined. In this study a unique morphological feature, a so-called suprapubic nodule, was seen in one cadaver, which lead to further investigations.
A longitudinal study during and after pregnancy documented natural ultrasonographic changes occurring at the pubic symphysis in 28 primigravidas (mean age 28 years, range 18-36 years). Participants were scanned during each trimester and twice post-partum, measuring ultrasonographic anatomical parameters established in the healthy volunteer study. Measurements for wide and narrow pubic symphysis widths and SPL depth increased slightly, but not significantly between the 1st and 3rd trimester and decreased in the post-partum period. Values for the following ultrasonographic measurements taken in the 3rd trimester (mean 35 weeks gestation) compared to those taken at a mean of 14 weeks post-partum decreased significantly: narrow pubic symphysis width (p<0.00), wide joint width (p=0.02) and SPL depth (p=0.00). Data from healthy volunteers were incorporated in the analyses of results enabling comparison with pre-pregnancy data from nulliparous women.
Compared to previous cross-sectional ultrasonographic investigations in pregnant women of mixed parity, findings from this study provide unique longitudinal data for ultrasonographic anatomical changes at the pubic symphysis in primigravidas.
