Patent ID: 8382805

Claim:
A limited angulation bone screw assembly adapted to couple a spinal rod with a vertebra, comprising: a bone screw ( 10 ) comprising a threaded shaft ( 13 ) and an upper head portion ( 20 ), the upper head portion ( 20 ) being a substantially spherical surface ( 23 ) having flat surfaces ( 18 ) disposed on opposite sides of the upper head portion ( 20 ); a bushing ( 30 ) comprising an upper portion ( 31 ) having a seat ( 33 ) shaped to receive the spinal rod and shoulders ( 38 ) on both sides of the seat, and a lower portion ( 32 ) having a rounded surface ( 35 ) and a pair of opposing flanges ( 43 ) having inner planar surfaces ( 46 ) shaped to slidably couple with the spherical surface ( 23 ) and flat surfaces ( 18 ) of the bone screw ( 10 ) to restrict motion of the bone screw to a single plane; and a housing ( 50 ) having an upper portion ( 53 ) with a first opening ( 67 ), a lower portion ( 56 ) with a second opening ( 69 ), and a first axis ( 63 ) extending between the upper and lower portions, the upper portion ( 53 ) comprising two spaced apart arms ( 55 ), each arm comprising internal threads ( 61 ) and an internal groove ( 87 ) configured to receive the shoulder ( 38 ) of the bushing ( 30 ), and a U-shaped channel ( 74 ) extending along a second axis transverse to the first axis ( 63 ) adapted to receive the spinal rod, and the second opening ( 69 ) being sized to engage the upper head portion ( 20 ) of the bone screw ( 10 ); wherein the screw is insertable through the first opening ( 67 ) until the threaded shaft ( 13 ) extends through the second opening ( 69 ) and the upper head portion ( 20 ) engages the second opening ( 69 ); wherein the bushing ( 30 ) is insertable through the first opening ( 67 ) in a first orientation with the shoulders ( 38 ) being positioned between the spaced apart arms ( 55 ) until the shoulders ( 38 ) are proximate to the internal grooves ( 87 ), the bushing ( 30 ) then being rotateable to a second orientation with the shoulders ( 38 ) being inserted into the internal grooves ( 87 ) and the bushing seat ( 33 ) aligning with the U-shaped channel ( 74 ); and wherein the upper head portion ( 20 ) of the screw couples with the lower portion ( 32 ) of the bushing ( 30 ) and permits angulation of the housing ( 50 ) relative to the bone screw ( 10 ) in a plane including the first and second axis, wherein the bushing ( 30 ) further comprises a groove ( 39 ) adjacent the shoulder ( 38 ) for frictional engagement with the housing.