Load Changes on a Short-Segment Posterior Instrumentation After Transosseous Disruption of L3 Vertebra – A Biomechanical Human Cadaveric Study

Abstract

Study Design Biomechanical Cadaveric Study. Objectives Following the successful use of a novel implantable sensor (Monitor) in evaluating the progression of fracture healing in long bones and posterolateral fusion of the spine based on implant load monitoring, the aim of this study was to investigate its potential to assess healing of transosseous fractures of a lumbar vertebra stabilized with a pedicle-screw-rod construct. Methods Six human cadaveric spines were instrumented with pedicle screws and rods spanning L3 vertebra. The spine was loaded in Flexion-Extension (FE), Lateral-Bending (LB) and Axial-Rotation (AR) with an intact L3 vertebra and after its transosseous disruption, creating an AO B1 type fracture. The implant load was measured on the one rod using the Monitor and on the contralateral rod by strain gauges to validate the Monitor’s measurements. In parallel, the range of motion (ROM) was assessed. Results ROM increased significantly in all directions in the fractured model ( P ≤ 0.049). The Monitor measured a significant increase in implant load in FE ( P = 0.002) and LB ( P = 0.045), however, not in AR. The strain gauge – aligned with the rod axis and glued onto its posterior side – detected an increased implant load not only in FE ( P = 0.001) and LB ( P = 0.016) but also in AR ( P = 0.047). Conclusion After a complete transosseous disruption of L3 vertebra, the implant load on the rods was considerably higher vs the state with an intact vertebral body. Innovative implantable sensors could monitor those changes, allowing assessment of the healing progression based on quantifiable data.