You don't even need to suffer physical harm to have PTSD. As the name implies, it is distressed occurring after a traumatic experience. Let's say you survive a tornado unscathed. You can still have stress afterward.
It is PTSD when the stress felt afterward is prolonged. Most people bounce back and have resilience, but some never stop reliving the experience. By the way, constantly reliving the experience is a symptom. Survivors guilt can be another symptom. If your neighbors properties or lives were destroyed but you were fine, you may have some guilt afterward.
Can a traumatic injury also lead to PTSD? Yes. But, it is not the only cause. A lot of it has to do with the person's disposition before the event. Those who are pessimistic, feel helplessness, or less psychologically resilient are much more likely to get it.
The right help and resiliency tools can bring someone out of it a lot of the time.