Sending good thoughts to Buffy's mom, siblings, and Buffy!
I ditto what BlueGiants posted about not having enough pee in the bladder reservoir all the time, so then nothing comes out when you express. You don't want to overtax the bladder muscles and express too hard.
Tamm, disabled bunn #2 in our home, fell from a loft shelf at a young age or binky'd too high in the basement and slipped/slammed down on the uncovered concrete floor damaging her soft tissue and muscular system. So that sounds similar to the fall Buffy experienced. We express her bladder daily, along with disabled Karla. Ongoing for almost four years, although they can pee on their own as well. Expression helps with sludge concerns, and saves on laundry.
As BlueGiants and Randy noted the spinal stress and healing time are important factors to monitor.
Buffy's bones are all okay...
Whew!! You're on a healthy recovery start already!
Yup, amazing how mom bunny is listening to her little one and sensing his minor distress. Keep up the good work taking Buffy to the vet and touching base in here with us human guardians who have Infirmary Knowledge and experience with disabled, spinal trauma and muscular impairment bunns.
Look forward to what other things your vet will say. Don't give up hope.
A few minutes each day can keep Buffy's impaired muscles properly working, after he gets through initial healing phase. I hope you'll check in and let us know how he's doing.