An intervertebral distraction tool has a clamshell head with upper and
lower halves, each having a curvate outer surface and a flat inner
surface. The distal side of the head is hinged so that the head opens and
closes from the proximal side of the head. The hinge is a separating
hinge that allows the halves to not only angulate with respect to one
another about the hinge axis, but also to vertically separate from one
another at the hinge. A distraction separator has decreasing taper at its
distal end and a longitudinal bore that accommodates the elongate shaft
of the trial so that the separator can be moved longitudinally relative
to the shaft. Upon forward movement of the separator, the tapered upper
and lower surfaces engage the flat inner surfaces of the head, causing
the halves to angulate about the hinge axis of the head, thereby opening
the head.