I remember this one, it was in the Swedish Championships 2004. Rider Andre Nilsson spent two months in hospital after the crash, 23 days in intensive care.
Both riders were knocked unconscious, but the guy causing it got away with minor injuries.
André suffered from shoulder injuries, a broken collar bone, and maybe a broken pelvis. [edited] Also collapsed lungs and head injuries(internal bleedings)
A year after the crash he was again riding motocross