A fixation device for fastening a medical implant to a patient'3 s bone is provided which includes a fastener with a head member and a shank and a fixation member. The shank has threads along its whole length, and has an outside diameter greater than the width of the head member. The fixation member includes a bore for receiving the fastener. The bore has a diameter intermediate the width of the head member and the outside diameter of the threads of the shank. The head member of the fastener can thus be inserted into the bore such that the uppermost thread abuts against the underside of the fixation member to prevent the fastener from backing out.