I suppose you could in theory do CPR with your feet/legs. But you know if someone breaks a rib it can puncture the lungs and kill them, Yakou-san...
Some theories on why Yakou didn't want a prosthetic:
- It's not possible to make one strong enough to keep up with him (lol),
- if you did make one very strong and light enough to use, plus the pain/damage from an amputation, makes it hard to get used to using freely quickly enough
- It's not "elegant"
- He is a stubborn old man with a death wish