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 eight 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 eight 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 12.8Nmm). The resultant two-dimensional motions at the injury site (i.e. 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.