Surgical cutting instruments and methods of use are described. The surgical cutting instrument (100) comprises an instrument body (102) with a first attachment mechanism (106) at a distal end. A cutter (104) has a central core (110), a plurality of cutting formations (130, 136) and a plurality of lobes (112, 114, 116) extending from the central core. The central core has side walls (118, 120, 122) which define an entirely open mouth and the side walls include a second attachment mechanism (140, 142, 144) which can interact with the first attachment mechanism to releasably attach the cutter to the distal end of the instrument body. At least one cutting formation (136) is provided on an end outer face (138) of the cutter opposite the entirely open mouth.