Volume 9, Issue 2 (February 2012)
The Use of a Single-Level Construct Model to Evaluate Nonmetallic “Flexible” Rods
The current ASTM F1717 standard specifies the static and fatigue testing conditions for extradiscal spinal implant assemblies. For the lumbar region, the standard stipulates a vertebrectomy model for said tests. While this testing setup has proven effective in analyzing overall construct stiffness, yield load, and displacement for rigid constructs, there is a growing segment of products and cases which amendments to the standard might better represent. One opportunity to evolve the current standard is in integrating test parameters which address the greater flexibility of semirigid or flexible systems such as those made from polymeric or metallic-polymeric materials. Since these rods are considerably more flexible when compared to rigid metallic rods, they create unique testing challenges. In addition, the current standard lacks a specification for testing single-level constructs. Considering that the overall dynamics of single-level cases vary greatly from the current vertebrectomy model, a modification or creation of a standard is needed. For the two reasons presented above, a single-level “discectomy” model has been developed to consider these unique testing conditions.