A locking mechanism assembly to allow locking of a fastener in an orthopedic implant having its axis at a variable angle relative to the axis of a threaded through opening in the implant. The assembly includes a convexly rounded ring shaped locking insert which mates with the through opening. The head of the fastener includes a concentric flange that engages the locking ring into a locking relationship with the threads of the opening as the fastener is tightened into position. Preferably the locking ring is integral with the head of the fastener. The locking ring is made from a material that is more deformable than the material of the plate.
