Hydrostatic interbody

1. An intervertebral implant comprising an upper plate having an upper surface configured for engagement with a first vertebral body, a lower plate having a lower surface configured for engagement with a second vertebral body, and a chamber between the upper plate and the lower plate, the chamber surrounded by a fixed inner wall in the upper plate and a fixed inner wall in the lower plate, the upper plate forming a first passage extending through the upper surface to facilitate insertion of a first bone screw through the wall and the upper surface into a first vertebral body, the lower plate forming a second passage extending through the lower surface to facilitate insertion of a second bone screw through the wall and the lower surface into a second vertebral body, the upper plate axially movable toward the lower plate to reduce the volume of the chamber and increase the hydrostatic pressure on an osteogenic material in the chamber, the upper plate comprising a hollow plug having a lobe extending outwardly from the plug, and the lower plate comprising a socket having a notch, the socket adapted to telescopically receive the plug when the lobe is radially aligned with the notch to maintain radial alignment between the upper plate and lower plate and substantially prevent rotation of the upper plate relative to the lower plate.

2. The intervertebral implant of claim 1 , wherein one of the fixed inner walls comprises a contraction member.

3. An intervertebral implant comprising an upper plate having an upper surface configured for engagement with a first vertebral body, a lower plate having a lower surface configured for engagement with a second vertebral body, a chamber between the upper plate and the lower plate, and an osteogenic material under a hydrostatic pressure in the chamber, the upper plate forming a first passage extending through the upper surface to facilitate insertion of a first bone screw through the upper plate and the upper surface into a first vertebral body, the lower plate forming a second passage extending through the lower surface to facilitate insertion of a second bone screw through the lower plate and the lower surface into a second vertebral body, the upper plate axially movable toward the lower plate to reduce the volume of the chamber and increase the hydrostatic pressure on the osteogenic material in the chamber, the upper plate comprising a hollow plug having a lobe extending outwardly from the plug, and the lower plate comprising a socket having a notch, the socket adapted to telescopically receive the plug when the lobe is radially aligned with the notch to maintain radial alignment between the upper plate and lower plate and substantially prevent rotation of the upper plate relative to the lower plate.

4. The intervertebral implant of claim 1 , wherein the lobe is one of a pair of diametrically opposed lobes extending outwardly from the plug, and the notch is one of a pair of diametrically opposed notches formed in the socket, the socket adapted to telescopically receive the plug when the lobes are radially aligned with the notches to maintain radial alignment between the upper plate and lower plate and substantially prevent rotation of the upper plate relative to the lower plate.

5. The intervertebral implant of claim 3 , wherein the lobe is one of a pair of diametrically opposed lobes extending outwardly from the plug, and the notch is one of a pair of diametrically opposed notches formed in the socket, the socket adapted to telescopically receive the plug when the lobes are radially aligned with the notches to maintain radial alignment between the upper plate and lower plate and substantially prevent rotation of the upper plate relative to the lower plate.