Postpartum sacral stress fractures and pubic symphysis diastasis as under-recognized structural causes of low back and pelvic girdle pain.

Pelvic girdle pain (PGP) is common after pregnancy, but clinical attention mainly focuses on benign, self-limiting ligamentous and muscular disorders. This narrative review highlights postpartum sacral stress fractures and postpartum pubic symphysis diastasis (PPSD) as under-recognized structural causes of severe postpartum low back and PGP and situates them within a postpartum pelvic ring instability spectrum (bony stress fractures and ligamentous disruption, with or without posterior ring injury). We narratively reviewed the English-language literature from 1980 to 2025 on sacral stress or insufficiency fractures and PPSD with symptom onset within 12 months after delivery, including case reports, case series, observational studies and existing guidelines. Postpartum sacral fractures typically present in the early postpartum period with sudden, load-related low back or buttock pain. Plain radiographs are often normal, whereas MRI reliably demonstrates sacral ala fractures and bone marrow edema. Management is usually conservative with protected weight-bearing, analgesia, bracing, and evaluation for pregnancy- and lactation-associated osteoporosis where appropriate. PPSD usually manifests within hours to a few days of delivery with disabling pubic pain and difficulty in weight-bearing. Diagnosis relies on correlating symptoms with symphyseal widening on pelvic imaging. Most women experience improvement with pelvic binders, analgesia, and physiotherapy, but marked separation or clear pelvic ring instability may require operative fixation. Greater awareness, early MRI and targeted pelvic imaging, multidisciplinary care and prospective research are needed to reduce diagnostic delay and long-term morbidity.