An automatic technique for micro-drilling a stapedotomy in the flexible stapes footplate

This paper describes a technique for controlling the drill bit breakthrough during low-speed micro-drilling of a flexible bone element. The research reported focuses on the penetration of the stapes footplate at the boundary of the middle and inner ear where there is a need to minimize the penetration of the drill bit through the medial surface. The bone is of unknown thickness and compliance, and the efficiency of cutting is variable between specimens. An automated system is presented that is able to determine these unknowns, to detect the onset of breakthrough and to control drill protrusion beyond the medial surface. The methods used to determine and control the level of protrusion on breakthrough are described. It is reported that the drill bit protrusion beyond the medial surface is achieved to within 0.02 mm of the ideal position.