Computer-assisted surgery in posterior instrumentation of the cervical spine: an in-vitro feasibility study

Transarticular C1/2 screws are widely used in posterior cervical spine inst rumentation. The use of pedicle screws in the cervical spine remains uncomm on. Due to superior biomechanical stability compared to lateral mass screws , pedicle screws can be used, especially for patients with poor bone qualit y or defects in the anterior column. Nevertheless there are potential risks of iatrogenic damage to the spinal cord, nerve roots or the vertebral arte ry associated with both posterior cervical spine instrumentation techniques . Therefore, the aim of this study was to evaluate whether C1/2 transarticu lar screws as well as transpedicular screws in C3 and C4 can be applied saf ely and with high accuracy using a computer-assisted surgery (CAS) system. We used 13 human cadaver C0-C5 spine segments. We installed 1.4-mm Kirschne r wires transarticular in C1/2, using a specially designed guide, and drill ed 2.5-mm pedicle holes in C3 and C3 with the assistance of the CAS system. Hole positions were evaluated by palpation, CT and dissection. Forty-eight (92%) of the 52 drilled pedicles were correctly positioned after palpation , imaging and dissection. The vertebral artery was not injured in any speci men. All of the 26 C1/2 Kirschner wires were placed properly after imaging and dissection evaluations. No injury to vascular or bony structures was ob served. C1/2 transarticular screws as well as transpedicular screws in the cervical spine can be applied safely and with high accuracy using a CAS sys tem in vitro. Therefore, this technique may be used in a clinical setting, as it offers improved accuracy and reduced radiation dose for the patient a nd the medical staff. Nevertheless, users should take note of known sources of possible faults causing inaccuracies in order to prevent iatrogenic dam age. Small pedicles, with a diameter of less than 4.0 mm, may not be suitab le for pedicle screws.