The ability to use screws to hold the fractured vertebra in place is a recent development. Advances in computer technology and imaging techniques have made this type of surgery possible. But it is expensive, requires a large facility, and isn't available everywhere yet.
The advantage of screw fixation over fusion is the obvious restoration of neck motion. Surgery to repair a Hangman's fracture of the C2 vertebra is a delicate operation and very difficult at best.
Real-time imaging is needed to allow the surgeon to see the spine after the patient is placed in the prone (face down) position. A special machine called Iso-C(3D) sends signals to a computer navigation system. The images are displayed on a TV screen during the operation.
Afterwards, CT scans and X-rays are used to verify the position of the spine. Once a segment is fused, it cannot be reversed.