Figure 1

Schematic diagrams to illustrate the surgery procedure. (A) For unilateral facet interlocking, the distractor screw holes are drilled in the locked side of the vertebral body at the medial margin of the longus colli; the interspace is gradually widened to about 5–7 millimeter by carefully operating the Caspar distractor mechanism; and a periosteal elevator is inserted at the disc space to resolve facet interlocking by a slight distracting force. (B) For bilateral facet interlocking, the holes are drilled at the median line of the vertebral body; the interspace is gradually widened to about 5–7 millimeter by carefully operating the Caspar distractor mechanism; and a periosteal elevator is inserted at the disc space to resolve facet locking by a slight distracting force.