A surgical device includes a polyaxial surgical screw that includes an internally hollow tulip. The tulip includes two elongated rods which are parallel and mutually spaced apart, each elongated rod protruding from a side wall of the tulip and extending away from a first end of the tulip in a direction opposite to a second end of the tulip. The rods define a channel in communication with the first end for accessing the interior of the tulip. A locking unit can be reversibly mounted on the polyaxial surgical screw. The locking unit includes a tubular body which has an inner cavity and is adapted to be fitted about the elongated rods during a configuration of use of the surgical device. The tubular body has two mutually opposite protrusions which project into the inner cavity that are configured to face the channel and be mutually interposed.