Design of a surgical instrument for removing bone to provide screw access to a spinal fusion cage.

A surgical instrument to aid implantation of a range of lumbar spinal fusion cages has been developed. Once the cage is in position, the entrance to screw holes is partially blocked by the edge of the vertebral body. In order to insert fixation screws to secure the cage between the vertebrae, some part of the blocking edge has to be removed. Rongeurs are currently being used, but they can be time consuming and have the disadvantage that they may remove more bone than is necessary and may cause damage to the fusion cage if not used with care. In addition, access around some of the screw holes may be difficult. The aim of this instrument was to overcome these shortcomings. This paper describes the design of a surgical instrument for cutting edges from vertebral bodies. The development and evaluation of concept designs are presented and discussed. Potential risks were considered and modifications were performed on the selected concept. Functional prototypes were manufactured and tested on sheep lumbar vertebrae. The results showed that the newly designed cutting instrument functions as required and removes the required amount of bone from the vertebral body edge.