The present invention is a one or two-part sleeve assembly for use during minimally invasive spinal stabilization surgery. An outer sleeve is designed to slide over the coupling between a polyaxial screw and an inner sleeve so as to prevent the screw from becoming disengaged from the inner sleeve during surgery. The outer sleeve includes a lower generally cylindrical wall having a slot, and an upper extension having an outwardly protruding manipulation handle attached to it. The slot in the lower section extends the entire length of the cylindrical wall, giving it a generally "C" shaped cross section. This slot corresponds with a similar slot on the inner sleeve for receiving a stabilizing rod to be attached to the polyaxial screw during surgery. The interior diameter of the lower section is approximately the same as the outer diameter of the inner sleeve, so that the outer sleeve may slide snugly over the inner sleeve and the screw coupling. In addition, the edges of the cylindrical wall adjacent to the longitudinal slot are flattened so as to conform to the shape of the inner sleeve and the head portion of the polyaxial screw where it couples with the inner sleeve.