Patent attributes
A bone screw assembly includes a tulip-shaped seat, a bone fixation device, a ring-shaped washer, a rod and a cap. The tulip-shaped seat comprises a through opening dimensioned to receive the bone fixation device and a horizontal channel dimensioned to receive the rod. The washer is placed into the seat on top of the bone fixation device head and comprises first and second side tabs and a first pair of upward extending projections separated by a first gap and a second pair of upward extending projections separated by a second gap. The side tabs interface with a groove formed in the bottom portion of the seat. The rod is placed within the channel and positioned within a groove formed on the top surface of the washer. The cap includes first and second projections extending downward from its bottom surface and each of the first and second downward projections comprises first and second sidewise extending ridges. The first ridges of the first and second projections are aligned and placed within the first and second gaps of the washer, respectively, and interface with a first groove formed on the side portion of the seat and the second ridges interface with a second groove on the side portion of the seat when the cap is rotate.
