US Patent 7699881 Bone screw

The invention concerns a bone screw comprising a head (2), a stem (3) and a thread (4) provided in the form of turns on the stem (3). A plurality of first turns (6) comprising smooth cutting edges (7) extend towards the head (2) from the free end (5) of the stem (3). Second turns (8) adjacent to the first turns (6), arranged in steps towards the head (2), comprise recesses (9) provided in the cutting edges (7). The size of the recesses (9) of the second turns (8) gradually increases from the free end (5) while the are of the edges in the peripheral direction gradually decreases.