Biomechanical evaluation of cervical spinal stabilization methods in a human cadaveric model.

The authors have previously reported in vitro testing of various posterior and anterior constructs (sublaminar, Rogers', and Bohlman's triple-wire wiring; AO hook plate fixation; and Caspar anterior plate fixation) in a bovine model with multiaxial biomechanical testing. This study was undertaken to evaluate the above constructs and other constructs in human cadaveric spines. Six subaxial human cervical spine specimens were biomechanically tested at the C5-C6 motion segment both intact and with a simulated distractive-flexion Stage 3 injury created at the C5-C6 level with complete disruption of the supraspinous ligament, interspinous ligament, ligamentum flavum, posterior longitudinal ligament, and facet joint capsules; with sufficient disruption of the intervertebral disc to allow a bilateral C5-C6 facet dislocation. The specimens were tested with a six-channel Bionix MTS 858 materials tester (M.T.S., Minneapolis, Minnesota) using cyclic loads to simulate cervical compression, flexion, extension, and rotation with measurements of axial load, axial displacement, torque, rotation, and anterior and posterior strains. Eight constructs were tested nondestructively: the intact spinal segment, sublaminar wiring, Rogers' wiring, Bohlman's wiring method (triple-wire technique), Roy-Camille posterior plate fixation, AO posterior hook-plate fixation, Caspar anterior plate fixation, and AO posterior hook-plate with Caspar anterior plate fixation. There was no significant difference in flexural stiffness and torsional stiffness between any of the constructs tested; however, there was a significant (P less than 0.05) increase in the posterior strain during flexion and axial loading tests between the Caspar plate construct and all other tested constructs, including the combined posterior and anterior plating construct. These differences persisted after cyclic testing of 100 cycles. Biomechanical testing demonstrated no significant differences between any of the posterior stabilization methods tested. Caspar anterior plating is clearly an inferior method of treating distractive flexion injuries of the cervical spine when compared with all posterior fixation techniques. Also, there is little biomechanical justification for the use of potentially dangerous sublaminar wire fixation and posterior plating methods in these injuries (with intact bony posterior elements), since the relatively safe interspinous wiring methods (Rogers' and Bohlman) are just as rigid as these other posterior fixation techniques.