Surgical instrument (1) comprising a longitudinal shaft (2) with a tip portion (3), a rear portion (4) and a longitudinal axis (5) and rotatable in the clock-wise and in the counter-clockwise direction around the longitudinal axis (5), said surgical instrument (1) further comprising: A) first means (6) for drilling a hole in a bone by rotation of the shaft (2) in one of the two directions B) second means (7) for crushing bone tissue when the shaft (2) rotates in the other of the two directions and C) a torque sensor (10) coupled to the shaft (2). Method for measuring the local mechanical resistance of a porous body comprising the steps of: a) drilling a hole to a desired depth into a porous body by advancing and rotating the shaft (2) in a first sense of rotation, preferably clockwise so that said first means (6) are active b) hammering the shaft (2) gently further into the porous body as far as the tip portion (3) of the shaft (2) has reached a desired measuring position and c) performing the torque measurement by rotating the shaft (2) in the opposite second sense of rotation, preferably counter-clockwise so that said second means (7) are active.
