Spinal fixation system

Apparatus for use in surgery for the correction or alleviation of spinal defects, comprises a number of pedicle screws and associated parts including a common correction rod clamped between the screws. Each screw has a slotted head (12) with a semicylindrical bottom wall (14). The slot has a partially threaded bore (16). In use, a plurality of screws are secured into adjacent spinal bodies. The slots (12) of the screws are aligned before inserting the common rod (20) into each slot to link the screws together. A pad (22), contoured to fit the profile of the rod (20), is next introduced into the bore (16) of each screw by use of a special tool to which it is screwed. When a pad has been introduced the tool is unscrewed from the pad leaving the pad in place. A threaded plug (34) is then screwed into the bore (16) of each screw to urge the pad (22) against the rod (20), to clamp the rod. The apparatus also comprises an instrumentation kit and novel tools to facilitate use.