Fig. 1

The instruments for creating defects in articular cartilage. a The disassembled crown mill—left the inner rod, right the cutting device—is equipped with a hand screw on top (b) for adjusting the desired depth of the circular groove. b The depth of the defect can be adjusted with a resolution of 50 μm using the scale with 10 steps. c The front mill consists of two parts, the cutting device (left) and the sleeve with an outer diameter of 6 mm that fits exactly into the circular groove prepared by the crown mill. Both instruments need to be turned clockwise