Improving stability of atlantoaxial fusion: a biomechanical study

Purpose The incidence of atlanto-axial injuries is continuously increasing and often requires surgical treatment. Recently, Harati developed a new procedure combining polyaxial transarticular screws with polyaxial atlas massae lateralis screws via a rod system with promising clinical results, yet biomechanical data is lacking. This biomechanical study consequently aims to evaluate the properties of the Harati technique.Methods Two groups, each consisting of 7 cervical vertebral segments (C1/2), were formed and provided with a dens axis type 2 fracture according to Alonzo. One group was treated with the Harms and the other with the Harati technique. The specimen was loaded via a lever arm to simulate extension, flexion, lateral flexion and rotation. For statistical analysis, dis-location (degrees) was measured and compared.Results For extension and flexion, the Harati technique displayed a mean dislocation of 4.12 degrees +/- 2.36 degrees and the Harms tech-nique of 8.48 degrees +/- 1.49 degrees (p < 0.01). For lateral flexion, the dislocation was 0.57 degrees +/- 0.30 degrees for the Harati and 1.19 degrees +/- 0.25 degrees for the Harms group (p < 0.01). The mean dislocation for rotation was 1.09 degrees +/- 0.48 degrees for the Harati and 2.10 degrees +/- 0.31 degrees for the Harms group (p < 0.01). No implant failure occurred.Conclusion This study found a significant increase in biomechanical stability of the Harati technique when compared to the technique by Harms et al. Consequently, this novel technique can be regarded as a promising alternative for the treatment of atlanto-axial instabilities