An implant that allows immobilization of one vertebra in relation to another, having two lateral walls essentially parallel one with respect to the other and having a length, and at least one transverse wall connecting these lateral walls one to the other, at least one of these lateral walls having, on its side facing the side opposite the other lateral wall, slide prevention reliefs. The invention, the implant has, in a direction perpendicular to the length of the lateral walls, a dimension such that its two lateral walls are capable of coming into the immediate vicinity of the unci of the underlying vertebrae, the slide prevention reliefs of each of lateral wall thus being able to bear against the internal surface of the uncus of the underlying vertebra adjacent this lateral wall.
