PURPOSE OF THE STUDY: Transarticular C1-2 fixation is a surgical alternative in treatment of atlantoaxial instability. Although the method provides very good immediate and long-term stability, it still involves several disadvantages. The group of patients as reported from various institutions are usually very small and hardly comparable. In order to objectively compare the results of the method, we collected the groups of patients treated in four institutions dealing with surgery of the cervical spine in Czech Republic. MATERIAL AND METHODS: During the 9-years period (1993-2001), the transarticular C1/2 fixation was performed in 80 patients (mean age 45.6 years, range 4-85 years). The procedure was indicated for atlantoaxial instability due to rheumatoid arthritis in 32 cases, pseudoarthrosis of the odontoid process in 15 cases, fracture of the odontoid in 8 cases, complex C1-C2 fracture in 7 cases, tumour in 5 cases, C1 fracture in 4 cases, os odontoideum in 3 cases, purulent osteolysis of the odontoid in 3 cases and instability due to tuberculosis in one case, respectively. Two patients underwent surgery for painful arthrosis of atlantoaxial joints only. Transarticular fusion was combined with posterior interlaminar fixation using autologous graft and wire in most of the cases. Clinical and radiological results were evaluated in the early postoperative period and 3, 6 and 12 months after surgery, respectively. The position of the screws in relation to lateral mass of the atlas was evaluated according to our own criteria as optimal, suboptimal, and misplaced. Long-term postoperative stability and bone fusion were also followed. The follow-up ranged from 3 to 99 months (mean 29.1 months). There were 72 patients available for long-term follow-up (i.e. more then 6 months). RESULTS: We inserted 150 screws; two screws were used in 72 patients, one screw in 6 patients while in two patients, the surgery had to be aborted without screwing. Optimal placement was achieved in 103 cases (68.7%), suboptimal because of too medial or lateral placement of the screws in 26 cases (17.3%), suboptimal due to a short screw in 9 case (6%) and a long screw in 8 cases (5.3%). Four screws (2.7%) were found misplaced (i.e. out of the lateral masses). Fusion was confirmed in 51 cases out of 72 operated on (70.8%) at 6-months follow-up, and in 55 cases out of 63 available for follow-up (87.3%) at 12 months, respectively. Segmental stability was achieved in all patients, even in cases with incomplete fusion as seen on radiograph. Furthermore, six screws in four patients were discovered to be broken, nevertheless without any clinical consequences. There were 4 cases of peroperative injury to th vertebral artery (i.e. 5% of patients, 2.7% of screws), one case of dural tear and one case of excessive blood loss from epidural venous plexus. These complications, however, did not cause any significant clinical consequences, either. Other postoperative complications included wound dehiscence in 3 cases, 2 cases of hardware failure due to wrong indication for surgery and 2 cases of persistent neck pain. DISCUSSION: Transarticular C1/2 fixation is known to be universal and stable technique suitable for the treatment of atlantoaxial instability. According to biomechanical studies, this method provides the best stability mainly in rotation and lateral flexion (inclination) when compared to other described methods of atlantoaxial fixation. The fusion rate is reported to vary between 90 to 100% if the posterior interlaminar fusion using bone graft and wire is simultaneously performed. The rare incidence of pseudarthrosis is usually considered to be related to a poor surgical technique as even only one screw should provide bone fusion if properly placed. Using strict evaluation criteria, the fusion rate in our sample of patients was 87.3% at 12 months, or, 92.1% if also controversial radiographs were included. The injury to the vertebral artery is the most serious complication of the method; its incidence in our group (5% of patients) is comparable to data from literature. We believe that most of these events happened because of individual anatomical variations of axis and vertebral artery were not adequately respected. CONCLUSION: Transarticular technique of instrumental atlantoaxial fusion is an effective method with multiple application in treatment of craniocervical and upper cervical spine instability. The gain of immediate stability with acceptable risk of possible complications is the major advantage of this procedure. The results of our multicentric retrospective study confirm the expected high fusion rate and are comparable to previously published reports.