Biomechanical Differences Between Transfacet and Lateral Mass Screw-Rod Constructs for Multilevel Posterior Cervical Spine Stabilization

Abstract

In vitro biomechanical investigation using human cadaveric cervical spines. Evaluate differences in biomechanical stability between typical lateral mass screw + rod constructs compared to transfacet screw fixation with and without rods. Lateral mass screw + rod constructs have reported efficacious arthrodesis rates/quality but risk damaging the lateral neurovascular structures. Transfacet screw fixation has been studied in the lumbar spine, but little data exists regarding its potential utility in the cervical spine. Sixteen human cadaveric cervical spines were stripped of soft tissue leaving the occiput and ligamentous structures intact. Spines were randomized to lateral mass or transfacet groups (n = 8/group). Spines were prepared in typical surgical fashion and instrumented with the appropriate devices. In the case of the transfacet constructs, the occiput was left intact to simulate the potential surgical difficulty of screw insertion. The transfacet screw group was initially instrumented with rods. Once instrumented (C3-C6) for each group, spines were further dissected to isolate the instrumented levels. End vertebral bodies were rigidly fixed and constructs biomechanically tested in flexion/extension, lateral bending, and axial torsion between +/-2 Nm. After testing for the transfacet screw + rod group, rods were removed and spines retested. All instrumentation was then removed and spines tested in their destabilized state as would occur with surgical preparation. Stiffness data were calculated for each test direction for all groups. Raw and normalized data were each compared across techniques with a 1-way ANOVA (P < 0.05). The transfacet screw groups (with and without rods) were found to have statistically similar biomechanical stability to lateral mass screw + rod constructs for each test direction. Transfacet screws (without rods) were found to have similar biomechanical stability compared to typical lateral mass screw + rod constructs. However, transfacet fixation eliminates the risk to the neurovascular structures and lowers the overall implant profile.