Clinical evaluation of three types of combined posterior atlantoaxial internal fixation techniques for treatment of atlantoaxial instability

Abstract

Objective To assess clinical curative effect of three types of combined posterior atlantoaxial internal fixation techniques in treatment of atlantoaxial instability. Methods The study involved 68 patients with atlantoaxial instability treated with different fixation techniques from August 2002 to March 2008. ( 1 ) Transpedicular fixation was performed in 32 patients including 20 patients with Anderson Ⅱ odontoid fractures (seven with old odontoid fracture and 13 with fresh fractures), six with type Anderson Ⅲ fresh odontoid fractures, four with disrupt of transverse ligament of the atlas and two with congenital loose odontoid process combined with atlantoaxial instability. (2) Transpedicular internal fixation with screws of atlas incorporating C2 laminar screws was performed in 20 patients with upper cervical injury including eight with type Ⅱ odontoid process fractures combined with atlantoaxial backward dislocation,four with type Ⅱ odontoid process fractures combined with atlantoaxial forward dislocation, two with nonunion of odontoid process fractures, three with type Ⅲ odontoid process fractures combined with atlantoaxial unsteadiness and three with atlantoaxial dislocation combined with disrupt of transverse ligament of atlas. (3)A total of 16 patients with traumatic atlantoaxial instability, reducible atlantoaxial dislocation and irreducible atlantoaxial dislocation were treated with four-point internal fixation technique using autologous iliac bone grafts. Results (1) A total of 120 screws were implanted in 32 patients, with no spinal cord or vertebral artery injury after surgery. Atlas lateral mass fixation was adopted in three patients because of broken posterior arch of the atlas. Postoperative CT showed that two screws were inserted into the vertebral artery hole and that one screw was inserted medially into the spinal canal and caused medial correx rupture, but both with no clinical symptoms. All 32 patients were followed up for 6-42 months ( average 26 months), which showed solid fusion in all patients. The postoperative JOA scores ranged from 13.2 points to 16.8 points (average 14. 8 points). (2) Thirty-two screws were implanted in 20 patients,with no spinal cord or vertebral artery injury. The patients were followed up for mean six months ( range 6-14 months). Postoperative X-ray showed sound bone fusion, with no cervical instability, loosening or breakage of the screws. (3) The symptoms of all the patients were improved at different degrees, with no neurological deterioration or severe complications, such as nerve blood vessel injury. All 16 patients were followed up for 8-26 months ( average 16 months), which showed bony fusion in all patients at 3-6 months after surgery. The spinal cord function was improved markedly in five patients, good in eight, mild in two but unchanged in one. Conclusions Three types of combined posterior atlantoaxial internal fixation techniques have advantages of rigid, short-segmental and three-dimensional fixation and hence are effective methods for treatment of upper cervical injuries. The combination mode can be varied according to specific condition of the patients. Key words: Atlanto-axial joint; Joint instability; Internal fixation; Spinal fusion