[Peripartum changes of the pelvic ring: usefulness of magnetic resonance imaging]

Postpartum pelvic pain beyond the normal level poses a problem to obstetricians. Beyond normal physiologic loosening of the pubic symphysis and sacroiliac joints (SIJs) during pregnancy, symphyseal separation and rupture must be excluded. The aim of this prospective study was to determine whether magnetic resonance imaging (MRI) allows for reliable differentiation of normal postpartum findings and pathologic lesions.

The study included a total of 77 women (mean age 30), among them 21 healthy subjects (group A), 21 asymptomatic postpartum women (group B), and 35 patients with postpartum pelvic pain (group C). The analyzed parameters comprised symphyseal and iliosacral tenderness, subjective pain assessed on a visual analog scale, and data pertaining to obstetric history. All 77 women underwent 1.5T MRI of the pelvic ring using oblique angulated coronal T 1-weighted and STIR sequences for imaging of the symphysis and SIJs in one slice package. Analysis of the MR images comprised signal intensities of pelvic bone marrow, width of the symphyseal cleft, and the symphyseal capsule.

Subjects in group A in general had a normal bone marrow signal. The STIR sequence showed increased signal intensity of the pubic bone near the symphysis in 16 women (76 %) of group B and 31 patients of group C (86 %) (not significant). An increased periarticular bone marrow signal of the SIJs on the STIR images was seen in 13 women (62 %) of group B and 23 patients (63 %) of group C. The mean width of the symphyseal cleft differed significantly among the three groups (3.4 mm vs. 5.4 mm vs. 6.7 mm). A width >10 mm was observed in only 4 cases (11 %). Moreover, associated findings such as interpubic hematoma (n=23) or tears of the symphyseal capsule (n=7) were detected in patients of group C.

The wide overlap of findings between symptomatic and asymptomatic postpartum patients does not allow reliable differentiation by MRI of normal and abnormal findings. MRI contributes to the differentiation of symphyseal contusion and rupture and provides information on severe associated changes.