Study design: Cadaver study. Objective: To examine whether C1–C2 intrafacet spacers (IFSs) contribute meaningful stability when added to traditional posterior instrumentation constructs. Summary of background data: 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. Methods: 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. Results: 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. Conclusions: 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 of Evidence Level V.
Hamrick et al. (Thu,) studied this question.