Morphological and clinical feasibility of C3 pedicle screw instrumentation in patients with congenital C2-3 fusion

Congenital C2-3 fusion (C2-3CF) is often involved in patients with atlantoaxial dislocation, and posterior occipitocervical fixation surgery is usually required. Hypoplasia of C2 pedicle is common in such patients, making C2 pedicle screws (PS) instrumentation inapplicable. Because of congenital fusion, C3PS instrumentation would be an ideal alternative for it will not sacrifice an additional motion segment; however, the morphological and clinical feasibility has not been previously reported. We included 42 C2-3CF patients to this study and evaluated pedicle trajectories of C2 and C3 using a three-dimensional CT. Clinical applications of C3PS instrumentation were evaluated and followed. Among the 42 patients, 23 (54.8 %) and 8 (19.0 %) had C2 and C3 pedicle trajectory diameters < 4.0 mm, respectively. The bisection line of the fused C2-3 lamina was used to represent the superior border of C3 articular mass; the entry point of C3 pedicle was located at 3 mm inferior to the assumed superior border and 3.2 mm medial to the lateral border. Bilateral C3PS instrumentations were successfully adopted in 22 patients. No spinal cord or vertebral artery injury occurred; postoperative CT showed a trajectory breach rate of 17.4 % for C3PS. After mean of 3.6-year follow-up, no implant failure was documented. C3PS instrumentation is morphologically and clinically feasible for a large proportion of patients with C2-3CF and can serve as another reliable alternative for C2PS instrumentation. Preoperative evaluation of pedicle trajectory of C2-3CF with three-dimensional CT is highly valuable in the choice of proper fixation methods.