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.

Anterior-to-Posterior Migration of a Lumbar Disc Sequestration: Surgical Remarks and Technical Notes about a Tailored Microsurgical Discectomy

“…Nevertheless, microdiscectomy induces an increased ROM in axial rotation and lateral bending [16]. However, conclusive data about the natural history and possible progression of an “overlap” instability syndrome of degenerative plus iatrogenic pathogenesis are still widely missing.…”

“…Interspinous fusion devices can be employed in both stand-alone mode or supporting interbody fusion with cages [17–19]. The dynamic fusion achieved is biomechanically complete, such as other fixation devices [16, 19]. These implants reduce the load over facet joints, reduce intradiscal pressure [20, 21], and have been found to decrease abnormal iatrogenic postdiscectomy increase in ROM in flexion-extension and in axial rotation and lateral bending, thus helping to preserve spine stability in the long run.…”

Perspective of Lumbar Segmental Instability for Surgical Evalua tion of Lumbar Disc Herniation

“…Additionally ISD has higher incidence of long -term reoperation and might lead to burden of cost [20,21]. Furthermore biomechanical changes such as decrease in ROM, and increase of interdiscal pressure and facet load at the adjacent segment following implantation of ISD are reported in both finite element and in vitro biomechanical studies [22,23]. ISD implantation causes to kyphotic position, segmental tilt and changes at instantaneous axis of rotation at the level of surgery.…”

“…ISD implantation causes to kyphotic position, segmental tilt and changes at instantaneous axis of rotation at the level of surgery. Therefore ISD implant could cause adjacent level facet pain or accelerated facet joint degeneration [23].…”

Comment on “Controversies about Interspinous Process Devices in the Treatment of Degenerative Lumbar Spine Diseases: Past, Present, and Future”

“…Another study [9] underlines that the distraction resulting by the placement of an IPD reduces the load of the posterior annulus in extension, neutral, and flexion position, but the load of the anterior annulus is increased about 400% due to distraction. This demonstrates that IPDs increase the risk of progression of disc degeneration.The implant of an IPD, whether restricted or not, causes an anterior overload in an already degenerated disc, accelerating the existing process and causing an acceleration of the instability [11]. …”