Serious injury

Injury requiring >48 hr hospitalization (within 7 days), a bone fracture (except fingers/toes/nose), severe hemorrhage/nerve/muscle/tendon damage, internal-organ injury, or 2nd/3rd-degree or >5%-body burns.

As taught in NTSB Accident and Incident Reporting (49 CFR Part 830) (Regulatory Framework and Pilot Responsibilities) — a free lesson with cited FAA sources.