The invention relates to an assembly for use in minimally invasive surgical procedures, including bone implant fixation procedures. The assembly is configured to provide a faster and more accurate measurement of depth of holes for placement of bone screws and fasteners. The assembly includes a guidewire having a deployable distal hook member configured to securely anchor into a desired position relative to a hole drilled in a bone and thereby provide an accurate datum for a measuring instrument for determining a depth of the hole for subsequent screw placement. The assembly further includes a surgical depth instrument to cooperatively function with the guidewire and obtain one or more measurements while operably coupled to the guidewire.