Advancing the design of interspinous fixation devices for improved biomechanical performance: dual vs. single-locking set screw mechanisms and symmetrical vs. asymmetrical plate designs

Interspinous devices were introduced in the field of spine surgery as an alternative to traditional pedicle screw fixation in selected patients for treatment of spinal stenosis and fixation. These devices designs have evolved from non-fixated extension blocks to sophisticated interspinous fixation devices (IFDs). There is an absence of literature comparing the biomechanical fixation strength of different IFD plate designs and the role of set screw locking systems. The aim of this study was to evaluate fixation strengths by bench testing static disassembly and pullout strength of two dissimilar IFD designs and locking mechanisms. We hypothesized that the InSpan (InSpan LLC, Burlington, MA, USA) dual-locking symmetrically IFD plate designed will have stronger fixation than the Aspen (ZimVie, Parsippany, NJ, USA) single-locking asymmetric IFD plate design.