Apparatus, consisting of a hinge (84), defining a hinge axis (88), and a pair of opposing jaws (80A, 80B) terminating at respective proximal regions and distal regions. The proximal regions are connected to the hinge so that at least one of the jaws is configured to rotate about the hinge between a closed state and an open state of the jaws. In addition, the jaws are curved in respective planes parallel to the hinge axis, and terminate in respective narrowed ends at the respective distal regions, wherein in the closed state the jaws are configured to grip one or more sections of vertebrae. The apparatus also has a support structure (60) that is configured to retain the hinge and the pair of opposing jaws. A multiplicity of sharp teeth (98) are disposed on respective inner surfaces of the opposing jaws.
