The use of Halifax interlaminar clamps in posterior arthrodesis for atlanto-axial instabilities has recently been reported. The four Anderson II fractures submitted were surgically treated by posterior arthrodesis with Halifax clamps and bilateral "H" shaped bone-grafts obtained from the iliac crest. Only in the first case--initially treated without fusion--a review of the system became necessary due to the loosening of one clamp. No post-operative neurological complications appeared and non malunion or nonunion occurred at follow-up. Posterior arthrodesis with Halifax clamps does not involve any complication connected with the use of metal wire and the association of posterior fusion by lateral "H" shaped bone grafts ensures a stable and physiological reduction of dens fractures and atlanto-axial luxations/subluxations often associated.