C1-C2 Stabilization: Do Intrafacet Spacers Add any Stiffness to Traditional C1-C2 Fixation?

Abstract

Cadaver study. To examine whether C1-C2 intrafacet spacers (IFSs) contribute meaningful stability when added to traditional posterior instrumentation constructs. The atlantoaxial (C1-C2) junction plays a pivotal role in cervical mobility, making surgical stabilization challenging. Traditional posterior instrumentation achieves significant stability but carries several notable risks. C1-C2 IFSs have been proposed as an adjunct approach to decompression and stabilization. Seven adult cadaveric specimens were subjected repeatedly to 7-axis biomechanical testing to quantify range-of motion (ROM) at the O-C3 complex after 6 sequential interventions: (1) intact baseline; (2) posterior C1 lateral mass and C2 pedicle screw construct; (3) addition of wired bone graft; (4) addition of IFS; (5) IFS with screw construct alone; and (6) IFS alone. Movements were normalized to baseline and compared using ANOVA with post hoc Tukey analysis. Posterior instrumentation (interventions 2-5) significantly reduced C1-C2 axial rotation (≤2% of baseline), flexion-extension, and lateral bending (all P<0.01). IFS alone (intervention 6) did not limit ROM and, in some cases, increased it. The stiffest construct involved traditional screw and rod instrumentation with both a wired bone graft and IFS. The traditional C1-C2 screw-rod construct provides substantial biomechanical rigidity. The addition of IFS may augment construct stability, but it is insufficient as a standalone stabilizer. Compared with the wired bone graft, IFSs provide equivalent rigidity when added to the C1-C2 screw and rod construct. Level V.