Machined cervical interfacet allograft spacers for the management of atlantoaxial instability

BACKGROUND: The use of cervical interfacet spacers (CISs) to augment stability and provide solid arthrodesis at the atlantoaxial joint has not been studied in detail. The aim of this work is to report the outcomes with the use of machined allograft CISs at C1-2. METHODS: A retrospective review of 19 patients who underwent an atlantoaxial fusion with the use of CISs was performed. All patients had instability documented with flexion and extension lateral radiographs. This instability was due to trauma, degenerative stenosis, symptomatic C1-2 arthropathy, and os odontoideum. Clinical and radiological outcomes were assessed. Fusion was determined based on a lack of hardware failure, absence of motion on flexion and extension plain X-ray films, and presence of bridging trabecular bone which was most often demonstrated by a computed tomography. RESULTS: The mean age was 69.1 ± 12.9 years. Eight patients had traumatic fractures, six patients had degenerative stenosis, two patients had C2 neuralgia due to C1-2 arthropathy, two patients had C1-2 ligamentous subluxation, and one patient had an unstable os odontoideum. The occiput or subaxial spine was included in the arthrodesis in 10 patients. Rib autograft was utilized in most patients. No patient had postoperative neurological worsening, malposition of hardware, or vertebral artery injury and there were no mortalities. The fusion rate was 95%. The mean follow-up was 12.1 ± 5.5 months. CONCLUSIONS: CIS is a promising adjuvant for the treatment of atlantoaxial instability.