Pedicle Screw System may not Control Severe Spinal Rotational Instability.

STUDY DESIGN An in vitro biomechanical study OBJECTIVE.: The purpose of this study is to discuss whether pedicle screw systems can control spinal rotational instability in a functional spinal unit (FSU) of lumbar spine on human cadaver. SUMMARY OF BACKGROUND DATA Rotational experiments using deer lumbar cadaveric models showed that rotational range of motion (ROM) of the model fixed by a pedicle screw system with crosslinking after total facetectomy for both sides was larger than that in the intact model, and stated that spinal rotational instability could not be controlled using a pedicle screw system. METHODS A rotation experiment using ten FSU (L3-4) of lumbar spine on human cadavers was performed by preparing the four models (intact model, damaged model, pedicle screw (PS) model and crosslink (CL) model) in stages, then calculating and comparing rotational ROM among the four models. RESULTS Rotational ROM in the CL model was still larger than that of the intact model in all samples. And, rotational ROM decreased in the order of damaged model >> PS model > CL model > intact model. Statistical analysis revealed significant differences between all models (p < 0.001). CONCLUSIONS Pedicle screw systems may not control severe spinal rotational instability in human lumbar cadaveric models with total facetectomy on both sides. This may represent a major biomechanical drawback to the pedicle screw system. LEVEL OF EVIDENCE N/A.