Bright red arterial bleeding with a mangled mess of a wound full of sharp bone fragments that preclude direct pressure? Tourniquet without a second thought. If possible, placed between the injury and the knee, though the OP makes it sound like I'd have to place just above the knee. While I'm talking care of the Massive hemorrhage, I'll have my partner take care of Airway and Respirations. Take care of any additional bleeding and check for head injury, then stabilize for immediate transport to local trauma center. For this patient that'd most likely mean log rolled onto a backboard with splinting and the rest of the secondary done enroute. (Hopefully one of the 50 fire medics we have on scene will have been talking to bystanders and will have found out the history, allergies, meds, and all that before we get that far.
We're allowed to realign long bones, in fact our county skills sheet considers it an error if we don't make an attempt to realign a severely deformed long bone if it's pulseless and cyanotic, so that'd happen when they're being placed onto the board. Once in back get a set of vitals, head to toe physical assessment. Once all that's done, depending on time to the TC, and how well our spider straps are keeping the leg secured, I'd be considering finishing off the splint by dressings the wound and securing with one of our vacuum splints (love those things, quick and easy to apply whether we're staying an playing on scene or headed down the road and they do the job better than our backup cardboard splints).
Just like the Sager on femur fractures, the fact that it's an open wound won't change how we do things. It's already got whatever nasty it's gonna get on it and leaving it open does nothing to help the patient and the trauma surgeons are still gonna do their thing to clean it all up, our job is to keep it stabilized so the sharp bone fragments don't move around and cut up more muscle, vessels or nerves.
