Complete head transplants are enormously complicated, requiring the reconnecting of literally millions of nerve fibers, not to mention bones and tissue. We're not really sure how any of this will work, but it looks like we're getting closer to a full this-head-on-that-body operation.
Sergio Canavero, a doctor at the Turin Advanced Neuromodulation Group, just published a paper looking at some recent developments in spinal cord fusion and suggesting that this means human head transplants are on their way. He puts forth a theoretical procedure that he says could enable these transplants. It involves a super-sharp cut right through the spinal column followed by mechanical fusion of the donor and recipient, held together with plastics like polyethylene glycol (PEG). He theorizes that the clean cut and tight fusion could allow the body to naturally repair the severed nerves.