Postpartum Sacral Stress Fracture Mimicking Lumbar Radiculopathy in a Patient With Pregnancy-Associated Osteoporosis

Postpartum sacral fracture is relatively rare, and its diagnosis is often delayed. We herein report such a case of a 28-year-old patient who presented with an insidious-onset lower back pain, left buttock pain, and radicular symptoms mimicking lumbar radiculopathy. Laboratory tests showed a decreased 25-hydroxy vitamin D level, and the bone mineral densitometry of both femurs was below the expected range. Plain radiographs of the lumbar spine and pelvis showed no definite abnormality, but lumbosacral spinal magnetic resonance imaging identified a left sacral fracture. Symptoms were alleviated with rest and oral analgesic treatment.