System and method for stabilizing the human spine with a bone plate

A spinal fixation system, comprising:

• a plate for stabilizing a spine, the plate comprising a borehole therethrough;
• a bone screw comprising a bone screw head and a bone screw shank, wherein a threaded portion of the bone screw head defines a cavity in the top surface thereof for receiving a lock screw;
• a ring positionable within the borehole and configured to receive the bone screw head;
• a lock screw sized to fit at least partially within the ring and comprising a lock screw head and a lock screw shank, wherein the lock screw shank is threaded in a manner complementary to the threaded portion of the bone screw that defines the cavity;
• wherein during use, the bone screw head is essentially contained within the borehole and the bone screw shank extends from the borehole to couple a plate to a bone, and further wherein the ring is rotatable within the borehole to allow the bone screw shank to be positioned at a plurality of angles substantially oblique to the plate during use, and further wherein the lock screw is configured to exert an expanding force against the ring during use, effective to substantially fix the bone screw with respect to the plate.