An implantable fixation assembly (30) for removably securing a (medical) device in a human body is disclosed. The assembly includes: an anchor portion (1) securable to bone; a pair of spaced apart legs (15), at least one leg (15) being resiliently flexible, the ends (15a) of the legs (15) attached to the anchor portion (1); a clamp portion (2) attached towards or at the ends (15a) of the legs (15); a screw and nut combination having an axis of rotation longitudinal to the legs, the combination operably engaging at least one of the legs (15) so as to pull them together or push them apart thereby actuating the clamp portion (2) to secure the device, wherein the actuating is reversible for selectively gripping and releasing the device.