Biomechanical Effect of a Lumbar Interfacet Cage (FFX) Device When Combined With Pedicle Screw Constructs: A Finite Element Study.

Abstract

<h4>Background</h4>Excessive stress on the pedicle screws or inadequate load-sharing with surrounding spinal components increases the mechanical demand and the risk of loosening or breakage. The lumbar interfacet cage (FFX device) is designed to prevent spinal instability and facet motion, enhancing facet joint fusion.<h4>Objective</h4>The present study aimed to compare the biomechanical performance of a lumbar interfacet cage when associated with a pedicle screw construct, compared with pedicle screws alone and pedicle screws associated with lumbar interbody cages, using the FE method.The authors hypothesized that implanting additional lumbar interfacet cages would reduce mechanical stress on pedicle screw constructs.<h4>Study design</h4>Comparative biomechanical study by finite element (FE) method.<h4>Methods</h4>A validated FE model for the lumbar spine was used to assess stress variations on pedicle screw constructs and discs in the prefusion stage following surgery. Modeled scenarios included (1) a short pedicle screw construct (L4/L5), with and without bilateral lumbar interfacet cage device placement and with or without interbody fusion cages, and (2) a long pedicle screw construct (L2-S1), with and without lumbar interfacet cage placement at all levels.<h4>Results</h4>Both facet and interbody cage placement in conjunction with short L4/L5 pedicle screw constructs significantly reduced mechanical loading on pedicle screws and rods compared with the pedicle screw construct alone. The placement of lumbar interfacet cages used in combination with pedicle screw constructs in long L2 to S1 constructs also significantly reduced stress loading on pedicle screws and rods, especially at the lower extremity of the construct.<h4>Conclusions</h4>The placement of facet cages in conjunction with pedicle screws can improve the load distribution of the construct, enhancing its stability and durability. This approach may help reduce the rate of pedicle screw loosening and breakage, which are complications commonly associated with long pedicle screw constructs.<h4>Clinical relevance</h4>Pedicle screw loosening and breakage remain frequent complications in lumbar fusion, especially in long constructs. This finite element analysis demonstrates that adding lumbar interfacet cages to pedicle screw constructs significantly reduces mechanical stress on screws and rods. By improving load distribution in both short and long constructs, the technique may decrease the risk of screw loosening and implant failure before fusion, potentially improving construct durability and reducing reoperation rates.<h4>Level of evidence: 5</h4>