System of a guide piece and milling cutter

System comprising a milling cutter and guide piece,

• the milling cutter comprising
• an elongate shaft extending along a longitudinal axis and a distal end portion having a milling part comprising at least one circumferentially disposed cutting edge for removing bone tissue,
• the guide piece having
• a fixation element, for releasably fixing the guide piece to a support structure, and a longitudinal axis
• wherein one of the guide piece and the distal end of the milling cutter comprises a head having a central axis coaxial to the longitudinal axis of said one of the guide piece and the distal end of the milling cutter, and the other of the guide piece and distal end of the milling cutter comprises a inner cavity extending along a central axis coaxial to the longitudinal axis of said other of the guide piece and the distal end of the milling cutter, said head comprising a guide portion having a bearing surface which is convexly rounded in the axial plane of the head, and said cavity comprising a guiding portion having an abutting surface which is concave in the axial plane of the cavity, said bearing and abutting surfaces being circular symmetric about their central axes, the cavity being sized and shaped to receive the guide portion of the head such that the convexly rounded bearing surface and concave abutting surface contact one another so as to permit simultaneous relative rotational movement between the head and the cavity about their central axes and pivoting of the longitudinal axis of the milling cutter with respect to the longitudinal axis of the guide peice.