Biomechanics of interspinous devices

Abstract

A number of interspinous devices (ISD) have been introduced in the lumbar spine implant market. Unfortunately, the use of these devices often is not associated with real comprehension of their biomechanical role. The aim of this paper is to review the biomechanical studies about interspinous devices available in the literature to allow the reader a better comprehension of the effects of these devices on the treated segment and on the adjacent segments of the spine. For this reason, our analysis will be limited to the interspinous devices that have biomechanical studies published in the literature.

Figure 1

Segmentary L5-S1 kyphosis of after the implantation of a stand-alone ASPEN interspinous device with overload of the anterior part of the intervertebral disc. (a) Sagittal balance of lumbar spine before the implantation of the ASPEN device: lumbar lordosis 48°, L4-S1 lordosis 33°, and L5-S1 lordosis 17°. (b) Sagittal balance of lumbar spine after 4 years from the ASPEN device implantation: lumbar lordosis 35°, L4-S1 lordosis 19°, and L5-S1 lordosis 8°. (c) MRI scan after 4 years from the Aspen implantation that shows anterior disc endplate degeneration (Modic II).