OPPORTUNITIES OF TRANSPEDICULAR SPINAL INSTRUMENTATION FROM THE POSITION OF BIOMECHANICAL MODELING

Objective. The authors analyze the causes of destabilization of transpedicular spinal instrumentation and prove the measures of its prevention basing on biomechanical modeling results and clinical data. Material and Methods. Experimental study included three series of 10 tests and one series of 12 tests with human spine cadaver specimens. The stability of injured spinal segments after transpedicular instrumentation was studied under mechanical load similar to that experienced by the human spine. Clinical study included the outcome analysis of transpedicular instrumentation in 107 patients with unstable thoracic and lumbar spine injuries. Results. The bone tissue mass around screws inserted in a cranial vertebra for two-segment spinal fusion proved to be the weakest place in a system consisting of a fourscrew transpedicular metal construction and spinal segments. The static mechanical strength of the injured vertebral motion segment stabilized with transpedicular device turned to be lower by 8–42 % (depending on loading conditions) than that of a corresponding intact vertebral motion segment. The identified factors negatively affecting the mechanical stability of transpedicular fixation were the following: osteoporosis, incomplete correction of deformity, motion coordination disorder due to neurological deficit, excessive weight, and postoperative regimen breach. A differentiated approach to reposition and transpedicular instrumentation for significant spinal deformities was offered allowing the restoration of anatomical interrelations and stable fixation in the spine regardless of the time of trauma.