Biomechanical evaluation of a bipedicular spinal fixation system: a comparative stiffness test

This biomechanical study using cadaver thoracic spines evaluated the initial stiffness of two different fixation constructs using a new spinal implant: the bipedicular spinal fixation device (BSF).

To compare the biomechanical stiffness of a new construct using BSF with a regular construct using pedicular and laminar hooks.

Disadvantages of thoracic posterior implants and developments in in situ rod contouring led to the creation of a new implant for spine deformity surgery that would provide immediate stiffness to preserve spine correction, allow efficient postoperative rehabilitation, and obtain a good fusion rate.

Two age-paired groups of six human thoracic spines each (T3-T12) were compared: a regular group whose construct was in accordance with the Cotrel-Dubousset technique and the BSF group. In both groups, the spines were tested intact and then after injury. An injury was induced by transections of interspinous and anterior longitudinal ligaments and anterior discectomies. A three-dimensional ultrasonic measurement device, the Zebris 3D Motion Analyzer, was used to record the motion of the T6 relative to the T8 vertebra under loads, and to determine the ranges of motion (ROMs) between intact spines and the spine construct.

In flexion-extension, the regular construct showed a significantly greater mean of relative ROMs than the BSF construct for principal rotation (88% and 69% respectively, P = 0.015). However, no significant differences were demonstrated in any of the other motions.

The BSF construct showed stiffness similar to that of the regular construct, encouraging clinical investigation.