The invention relates to an implant device, comprising an actuating instrument (110) and a height-adjustable implant (10) having a substantially U-shaped inner basket (11) and a U-shaped outer basket (60), wherein the inner basket (11) of the implant (10) is embraced by the outer basket (60) and telescopically guided, and the inner basket (11) and outer basket (60) are equally aligned, and wherein the limb (12, 13) of the inner basket (11) and the limb (61, 62) of the outer basket (60) are aligned so that a substantially continuous lateral opening (80) results, and the inner (11) and outer (60) baskets can be fixed with respect to each other in a predetermined end position, and wherein vertebral support surfaces are provided on the end faces (18, 63) of the baskets (11, 60), wherein the actuating instrument (110) has a fixation rod (111) and an expansion mechanism with sliding elements (122), and the inner basket (11) and fixation rod (111) have corresponding elements (26, 112), by means of which a detachable, rigid connection between the fixation rod (111) and inner basket (11) is achieved, and wherein by actuating the expansion mechanism on the actuating instrument, the outer basket (60) can be moved in the longitudinal direction (L) by the engagement of the sliding elements (122) at the limbs (61, 62) opposite the inner basket (61).