Thanks for bringing this back up, there has been a TV series on in the UK called SuperVet and he is doing exactly what you suggest, he mounts metal feet permanently to the bone of cats, probably titanium as the bone then grows to it, the skin is then grown onto a mesh over it to seal the ends, a foot is then mounted onto this...
See
Oscar | Specialist Orthopaedics + Neurosurgery | Fitzpatrick Referrals
http://www.fitzpatrickreferrals.co.u...pisode-1/oscar