The invention relates to a self-retaining implant for fixing a bone cover or a bone fragment in an opening in a skull bone. The implant comprises a support element with an upper side and an lower side facing the bone cover. Arranged on the lower side of the support element is an extension, which supports a spike preferably extending parallel to the support element. The spike can be driven laterally into the bone cover or bone fragment by means of a driving-in device according to the invention. The driving-in device according to the invention comprises a receiving element for the implant. A driving-in mechanism for driving the implant into the bone cover or bone fragment can be coupled with the receiving element.