A screw for syndesis of a fracture, comprising a tubular stem (2) which can be inserted in a hole which passes through the fracture region and has, at one end, a threaded portion (3) and, at the opposite end, a substantially hemispherical head (4), an abutment ring (7) being arranged on the stem (2) and being mated with the head (4) so as to provide a spherical coupling which is suitable to allow the ring (7) to rest flat on the region of the cortex that surrounds the hole in which the stem (2) is inserted.
