Hi there. Your fiance suffered from condition called atlantoaxial dislocation which was pressing on nerves and surgery had to be done to release the nerve compression which could have lead to quadriparesis. Now there won't be any problem related to that condition as already fixation of sad is done, there may be some residual weakness because of which he is limping. In future he might have degenerative diseases of spine early than others. Doing Regular exercises will keep check on his health issues.. you may consult neurosurgeon/ orthopedician once.