Impact of C1 assimilation on C2 pedicle screw insertion

Abstract

Objective To study the impact of C1 assimilation (C1 A) on C2 pedicle screw insertion,and variation of C2 screw insertion techniques. Methods Seventeen C1 A patients which needed C2 pedicle screw insertion and fixation were collected, including 14 cases of atlantoaxial dislocation and 3 cases of Chiari malformation. All patients underwent thin slice CT scanning. The C2 pedicle screw was virtually inserted by using computer-assisted navigation, and the maximum pedicle screw diameter (MPSD), which could be inserted without breaching the C2 pedicle cortex was measured in 3-plane reconstruction. All patients underwent surgery according to the measurement. Results In C1 A group, the mean MPSD of 34 pedicles was (5.8 ± 1.4)mm; and in 5 of 34 (15%) pedicles, the MPSD was less than 4 mm. In non-C1 A group, the mean MPSD of 50 pedicles was (6. 5 ± 1.4) mm; and in 4 (8%)pedicles, the MPSD was less than 4 mm. The mean MPSD had statistical significance between two groups (P ＜ 0. 05). For patients not suitable to C2 pedicle screw insertion, the fixation was executed by extending the fixation to C3 in 2 patients,by using C2 pars interarticularis screw in 2, and inter-laminar screw in 1. Conclusions C2 pedicle in C1 A patient is relatively narrower; more attention should be paid, or alternative screw insertion techniques can be used. Key words: C1 assimilation; C2pedicle; Screw insertion