Sounds like compartment syndrome. Very serious.
If he shows signs of compartment syndrome he will have a fasciotomy to relieve the pressure. It’s possible they wanted to stabilize him before an orthopedist took him to the OR to fix the fracture. Or maybe he’s already had the fracture reduced with an internal rod and/or pins in which case regular washout of the wound is standard protocol.
I don’t think he’d have compartment syndrome if he had an open fracture, because the fascia would be “opened” by the bone sticking through it. At least that’s what I’m thinking. Lots of blood loss could lead to some tissue, muscle, etc., death, which would have to be cleaned out regularly.