a bone reamer has an ablation device for forming cavities in body tissue , the ablation device is movable with respect to a head of the reamer , and is capable of protruding at least partially beyond a surface of the head . the amount of protrusion the ablation device protrudes beyond the surface of the head has a variable geometry and the geometry is remotely modifiable . more particularly , the amount the ablation device extends beyond the outer surface of a reamer head body can be varied by an actuator located on the reamer outside the body .