Design and biomechanical evaluation of a rodent spinal fixation device

Study design: An in vitro and in vivo study in rats. Objectives: To design a novel rat spinal fixation device and investigate its biomechanical effectiveness in stabilizing the spine up to 8 weeks post injury. Methods: A fixation device made of polyetheretherketone was designed to stabilize the spine via bilateral clamping pieces. The device effectiveness was assessed in a Sprague–Dawley rat model after it was applied to a spine with a fracture–dislocation injury produced at C5–C6. Animals were euthanized either immediately ( n =6) or 8 weeks ( n =9) post-injury and the C3-T1 segment of the cervical spine was removed for biomechanical evaluation. Segments of intact spinal columns (C3-T1) ( n =6) served as uninjured controls. In these tests, anterior–posterior shear forces were applied to the C3 vertebra to produce flexion and extension bending moments at the injury site (peak 12.8 Nmm). The resultant two-dimensional motions at the injury site (that is, C5–C6) were measured using digital imaging and reported as ranges of motion (ROM) or neutral zones (NZ). Results: Flexion/extension ROMs (average±s.d.) were 18.1±3.3°, 19.9±7.5° and 1.5±0.7°, respectively for the intact, injured/fixed, and injured/8-week groups, with the differences being highly significant for the injured/8-week group ( P =0.0002). Flexion/extension NZs were 3.4±2.8°, 5.0±2.4°, and 0.7±0.5°, respectively for the intact, injured/fixed, and injured/8-week groups, with the differences being significant for the injured/8-week group ( P =0.04). Conclusion: The device acutely stabilizes the spine and promotes fusion at the site of injury.