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.