A shoulder dystocia is a serious injury that can happen during childbirth. Though it can occur in a few different ways, it typically happens when the child's shoulders are not in the expected position as it is being born. Even so, the head is able to pass through the birth canal.
However, after the head emerges, the child becomes stuck. One shoulder gets caught on the pubic symphysis, which is an area of cartilage that runs between the left and right pelvic bones.