Patent ID: 8048124

Claim:
A bone screw assembly comprising: a tulip-shaped seat comprising a semispherical bottom portion and a cylindrical side portion extending upward from said bottom portion and wherein said bottom portion comprises a through opening dimensioned to receive a bone fixation device and to prevent the fixation device from passing entirely therethrough and wherein said side portion comprises first and second concentric grooves extending along its inside periphery wall and a horizontal channel dimensioned to receive a rod; a bone fixation device comprising a bone fixation portion passing through said bottom portion opening and a head residing within said semispherical bottom portion; a ring-shaped washer placed into said seat on top of said bone fixation device head and comprising a first pair of outward extending projections separated by a first gap and a second pair of outward extending projections separated by a second gap, wherein said projections extend from the top surface of said washer and are shaped and dimensioned to interface with said first concentric groove of said seat side portion; a rod placed within said channel and positioned within a groove formed on the top surface of said washer; and a cap comprising first and second projections extending downward from its bottom surface and wherein each of said first and second downward projections comprises first and second sidewise extending ridges and wherein said first ridges of said first and second projections are aligned and placed within said first and second gaps of said washer, respectively, and interface with said first groove of said seat side portion and said second ridges interface with said second groove of said seat side portion when the cap is rotate.