Design Rationale for Posterior Dynamic Stabilization Relevant for Spine Surgery

Abstract

Motion sparing posterior dynamic stabilization (PDS) devices have been introduced as an alternative to spinal fusion. A majority of these devices are based on instrumentation and techniques that surgeons are most familiar with, due to their experience with posterior fixation for spinal fusion. The goal of this new generation of devices is to allow controlled motion of the treated spinal segment that closely mimics physiologic spinal kinetics and kinematics, with the most common indication for use being spinal stenosis. The rationale for dynamic stabilization as an alternative to spinal fusion is to restore spinal stability, while avoiding (or delaying) degeneration of adjacent segments. Most commonly used PDS devices are either pedicle screw-based or interspinous process-based. The pedicle screw-based devices are commonly approved for use in spinal fusion, or as an adjunct to fusion, but not as stand-alone devices in the absence of fusion. Despite familiar surgical techniques and extensive preclinical testing, most pedicle screw-based PDS devices are still considered investigational for the treatment of disorders of the spine. One of the main reasons is that it is not yet clear whether PDS truly offer advantages over conventional spinal fusion or decompression alone, in terms of patient reported outcome scores. Other technical factors that pose a challenge for PDS devices are long-term fixation to the spine via pedicle screws or interspinous fixation, and variations in device stiffness, level of stabilization offered, and the range of motion allowed by PDS devices over time. This chapter presents an overview of in vitro testing methodologies used to evaluate PDS devices, followed by a summary of clinical performance of stand-alone dynamic stabilization devices with or without direct decompression.