A surgical machining instrument (10), especially a surgical drilling or sawing instrument, is used for determining the local mechanical resistance of a bone (50) in connection with the machining action. Therefore, the instrument comprises a first sensor unit adapted to determine energy expenditure during the machining action and a second sensor unit (30, 40) adapted to determine the volume of removed material during the machining action and being time synchronized with the first sensor unit. A control unit (20) is adapted to determine the applied specific energy as energy per volume of removed material over time based on the data of the sensor units and is furthermore adapted to convert the measured data in a value of the local mechanical resistance of said bone.
