Interspinous Devices: State of the Art

Abstract

Interspinous devices are in the class of medical devices that can be implanted in the lumbosacral spine using a minimal and often mini-invasive approach. Because their use has boomed over the last decade, we can state with confidence that this technological sector attracts a great deal of interest in a quest for techniques and materials able to reduce the invasiveness of the surgical procedure and increase its general bio-compatibility. An initial classification of interspinous devices from a biomechanical viewpoint may be carried out by assessing the rigidity of the distraction element (Table 1, Appendix). This identifies devices that are inaccurately categorized as nondeformable, involving the insertion of material with high mechanical rigidity into the space between the spinous process, where the distraction between the spinous processes may be considered constant. In other devices, a material with a shock-absorbing function is inserted between the spinous processes, which then undergoes appreciable elastic or visco-elastic deformation under physiological loads to increase bone implant compliance. In parallel with this sub-category, there are also devices that work by rigid stabilization of the interspinous space where stable posterior interspinous fusion is brought about by applying autologous or homologous bone and cruentation of the spinous processes. Clinical trials on interspinous devices available in the literature show a good relationship between the benefits for the patient and the use of resources in the disease treatment. Nevertheless, there is still margin for clinical investigation and for the establishment of verification and validation procedures of these devices in order to clearly define the relationship between the effects on the biomechanics of the functional unit and the clinical indications of such devices.