Oh no!
I have experience of this - several years ago Waffles had an altercation with a motor & her pelvis was broken in four places so it was completely detached from her spinal column.
So this is with that experience in mind.
Go to a pet superstore, such as Jollyes or Pets At Home and hire a dog/cat crate for six weeks. You know - the wire sort. Get one big enough to take Joe on a blanket, with his food/water dishes nearby and a small litter tray but not so big as he can move about a lot. Keep Joe confined to the crate for the duration. This way the break gets the chance to heal *properly*. Towards the end of the six weeks, Joe WILL be going stir-crazy, but long term it's best. The confined area is *essential* as it means the cat - at the start, doesn't have to move too far to get at food/water/litter tray. Plus, once the break(s) start to heal, animals can become over-confident and try to move too much/start jumping about and all too easily re-break the bones and cause a fracture to become unstable. This is seriously NOT GOOD long term if this happens.
I've heard too many times of cases where the cat/dog has a fracture and the owner doesn't do the cage/crate rest thing and the animal ends up having to be euthanised or have a limb amputated due to re-fracturing or the bonmes beoming unstable. And I'm so very glad I did put Waffles through cage rest as she healed *properly* after, as well as the multiple fractures of the pelvis, an open fracture of the femur, broken ribs and a fractured skull. She came out of it much better than too many with less severe injuries. She didn't appreciate the enforced cage/crate rest towards the latter stages, but I'm convinced it made a real difference to her recovery.
Hoping Joe recovers 100%