Abstract: This invention relates to segmental spinal instrumentation, specifically metal spinal hooks and rods used for the correction of spinal deformities such as idiopathic scoliosis. It includes an apparatus for use in retaining a longitudinally extending member in position relative to a spinal column. The apparatus is comprised of a body having an open ended recess which extends through the body and is open along one side to enable the longitudinally extending member, spinal rod, to be moved into the recess. The recess having a side opening, a first end opening formed in a first side of the body and intersecting the side opening, and a second end opening formed in a second side of the body opposite from the first side and intersecting the side opening to enable the longitudinally extending member to be moved into the recess through the side opening and to extend from the first and second sides of the body through the first and second end openings.