Mechanical and in Vitro Testing of a Biomechanically Fidelic, Compliant Mechanism Based, Motion-Preserving Lumbar Interbody Device

Abstract

A common approach to resolving discogenic low back pain involves replacing one or more degenerated spinal discs with a total disc replacement device. However, existing solutions for intervertebral disc replacement are unable to fully capture the kinetic and kinematic characteristics (i.e., the quality of motion) of the intact spinal disc. In the present work, a novel single-piece compliant mechanism driven, motion-preserving lumbar intervertebral implant design is described. Prototypes were manufactured from Ti6Al4V and evaluated using benchtop mechanical and in vitro biomechanical testing. ASTM F2346 static testing procedures were followed to assess the design's compressive, shear, and torsional properties. Similarly, the forces necessary to cause the device to be ejected from the interbody space and the force required to cause subsidence were tested. in vitro testing was conducted with fresh-frozen human cadaveric lumbar spinal segments to analyze the quality of motion of the intact segments and after they were instrumented with the compliant interbody device prototype. The design was robust in static compressive, shear, and torsional loading. Expulsion and subsidence test results were comparable to devices currently in use. in vitro testing indicated that when appropriately placed in the intervertebral space, the instrumented segment's quality of motion closely replicated the intact segment.