Biomechanical evaluation of C1 lateral mass and C2 translaminar bicortical screws in atlantoaxial fixation: an in vitro human cadaveric study

Background Context

Atlantoaxial fixation with C1 lateral mass-C2 translaminar bicortical (C1LM-C2TB) screws has been reported to afford good stability with the least risk of injury to vertebral artery. However, no comparative in vitro studies have been conducted to evaluate the biomechanical stability of this method.

Purpose

This study aimed to compare in vitro biomechanics of fixation with C1LM-C2TB with fixation with C1 lateral mass-C2 translaminar unicortical screws (C1LM-C2TU) and with C1 lateral mass-C2 pedicle screws (C1LM-C2PS).

Study Design

This is an in vitro biomechanical study.

Methods

Fifteen fresh-frozen human cadaveric cervical spines (C1–C3) were tested after destabilization by transverse-alar-apical ligament disruption. Instrumentation was performed with three fixation constructs: C1LM-C2PS, C1LM-C2TU, and C1LM-C2TB. Flexion, extension, lateral bending, and axial rotation were tested. Range of motion and neutral zone pre-fatigue and post-fatigue values were measured.

Results

No significant differences were observed in flexion-extension among the three groups. However, C1LM-C2TB fixation was superior to C1LM-C2TU fixation in lateral bending and axial rotation.

Conclusion

C2 translaminar bicortical screws are biomechanically superior to C2TU screws for fixation of the atlantoaxial complex, and it is equivalent to C2PS fixation. C2 translaminar bicortical screws or C2PS should be preferred over C2TU screws.