Classification of Posterior Dynamic Stabilization Devices
Numerous new posterior dynamic stabilization (PDS) devices have been developed for the treatment of disorders of the lumbar spine. In this report the authors provide a classification scheme for these devices and describe several clinical situations in which the instrumentation may be expected to play a role. By using this classification, the PDSs that are now available and those developed in the future can be uniformly categorized.

It is estimated that up to 50 million individuals in the US suffer from symptoms related to spinal degeneration, and that in 2004 more than 1 million spinal procedures were performed to alleviate or mitigate this condition. For the neurosurgeon treating this population, open surgical intervention has traditionally been directed at decompressive procedures to relieve neural element compression and/or fusion techniques to stabilize the spinal column.

Advancements in technology have added to the surgeon's armamentarium and necessitate new classification schemes. For example, widely adopted new surgical procedures, such as percutaneous vertebral augmentation (vertebroplasty and kyphoplasty) and total disc replacement, do not fit easily within the rubric of decompressive or fusion techniques.

One of the most rapidly evolving fields in spinal surgery is PDS. This new category of thoracolumbar spinal surgery focuses on the concept of maintaining or restoring intervertebral motion in a controlled fashion, whether by restricting the extremes of spinal movement or by dampening the kinetic energy involved in motion. The goal of these implantable devices is to mimic the behavior of the healthy spinal column (Fig. 1).



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Graph showing the load displacement curve of the intact spine compared with the degenerated spine, and the ideal concept of "restoring" normal motion of the degenerated spine with posterior dynamic devices.