A reamer for preparing a spinal upper facet to facilitate insertion of combined screw/washer implant, preventing bone damage and facet weakening, and also allowing possibility to place grafting so as to maximize implant stabilization. The reamer has shallow outer cutting surfaces to cut a groove for spike insertion; deep inner cutting surfaces to cut a cortical-penetrating bore for insertion of the screw, and a flat therebetween to limit penetration of these cutting surfaces.