1. Instrument for measuring the distraction pressure between vertebral bodies, with an adjusting device (34, 36 64, 66) for introducing a compressive force onto surfaces of opposed vertebral bodies, with a pressure-measuring device (50 84 184), assigned to the adjusting device (34, 36 64, 66 165), for determining the compressive force exerted on the vertebral bodies, characterised in that . at least one end region of the adjusting device (34, 36 64, 66 165) carries an abutment body (10 110) which is designed for engagement in a concavely vaulted dome of the vertebral bodies which is enclosed by an osseous ring, whereby the abutment body (10 110) is capable of swivelling about at least one swivel axis in relation to the adjusting device and/or has such a convexly vaulted abutment surface (16, 116) that upon engagement in the dome the abutment body is capable of swivelling about at least one swivel axis by sliding motion in relation to the vertebral body.
