This position might seem to put the child's legs at greater risk of injury in case of a car accident, but on the other hand, the rear-facing car seat offers much more protection to your child's neck and spine. Although choosing one potential car crash injury over another is never pleasant, leg injuries heal much faster and are not usually fatal as opposed to head, neck or spine injuries.
Anyhow, there are no recorded cases of children injuring their legs while seated in rear–facing car seats. But there are, however, many recorded cases of leg injuries with children in forward-facing car seats. And what is more, these injuries often come with quite severe or even fatal head, neck or spine injuries.