Biomechanical Stability of the Stalif-C Stand-Alone Spacer in Multi-level and Hybrid Cervical Fusion Constructs

Abstract

Introduction Anterior plate constructs for cervical discectomy and fusion have been linked to postoperative dysphagia, increased operative times, and wider surgical exposures. Several “low profile” integrated stand-alone spacers (SAS) have been developed. While these spacers have demonstrated successful clinical outcomes and similar biomechanical stability to anterior plate constructs in single-level fusions, their biomechanical stability in multi-level constructs has not yet been established. Methods Twelve human cadaveric cervical spines (C2-T2) were nondestructively tested with a six-degree-of-freedom simulator under axial rotation (AR), flexion-extension (FE), and lateral bending (LB) loading. After intact analysis, each specimen underwent sequential instrumentation and testing: (A) C5-6 spacer/plate with C6-7 SAS; (B) C5-7 SAS; (C) C5-7 spacer/plate. Range of motion (ROM) data was obtained and analyzed with paired t-tests and Bonferroni correction. Results The 2-level plate construct significantly reduced flexion-extension ROM compared to the 2-level SAS (5.6 ± 3.4 degrees versus 11.6 ± 4.6 degrees, respectively; p < 0.05). There was a significantly increased segmental ROM in the 2-level SAS construct compared to the 2-level hybrid construct in flexion-extension as well (11.6 ± 4.6 degrees versus 7.2 ± 2.4 degrees, respectively, p < 0.05). There was no significant difference in lateral bending and axial rotation ( p > 0.05) between the three different 2-level constructs. Conclusions Our study found that hybrid and 2-level SAS constructs are comparable to conventional anterior plate constructs in lateral bending and axial rotation, but there was an increase in flexion-extension motion allowed with constructs that incorporated a SAS. Stand-alone cervical spacers with integrated screws for hybrid and 2-level SAS constructs are reasonable alternatives to two-level plate fixation; however, clinical trials are necessary to determine if the increased ROM in flexion-extension noted in the SAS constructs translates to clinical outcome.