Unusual mode of mechanical failure of an AO cannulated self drilling screw. A case report.

Cannulated AO screws are commonly used for fracture fixation. Mechanical failure of screws has been well reported but this was mainly breakage of the screw head during removal. We report an unusual mode of failure of an AO self drilling cannulated screw which we have not previously experienced, where the screw threads were found to be unravelled during insertion. We also suggest the way to recognise this complication early and how to prevent or deal with it.