An adjustable device for defining a cutting plane for bone resection comprising a base positionable on the bone and a cut-guiding element placeable on the base. The cut-guiding element includes a cut-guiding structure for guiding a cutting tool in the cutting plane, the cut-guiding element being tiltable relative to the base about at least one first axis by an adjustable tilt mechanism to adjust the angle of the cutting plane. The tilt mechanism includes a rectilinear guide and a slide that is linearly displaceable along the guide in the longitudinal direction. The tilt mechanism includes a guide portion relative to which an effective portion of the slide is displaced the guide portion and the effective portion having interacting structures forming a sliding guide effective at a right angle to the longitudinal direction.
