Posterior atlantoaxial facet screw fixation.

Eighteen patients with atlantoaxial instability were treated with posterior atlantoaxial facet screws to obtain immediate rigid fixation of C1-2. Of these 18 patients, instability occurred due to trauma in nine, rheumatoid arthritis in six, neoplasms in two, and os odontoideum in one. Four patients presented with nonunion after failed C1-2 wire and graft procedures. In all cases in this series the screw fixations were augmented with an interspinous C1-2 strut graft which was wired in place to provide three-point stabilization and to facilitate bone fusion. In every case fixation was satisfactory, and C1-2 alignment and stability were restored without complications due to instrumentation. One patient died 3 months postoperatively from metastatic tumor; the spinal fixation was intact. All 17 surviving patients have developed osseous unions (mean follow-up period 12 months, range 6 to 16 months). Posterior atlantoaxial facet screw fixation provides immediate multidirectional rigid fixation of C1-2 that is mechanically superior to wiring or clamp fixation. This technique maximizes success without the need for a supplemental rigid external orthosis, and is particularly useful for pseudoarthrosis.