Femoral ring versus fibular strut allografts in anterior lumbar interbody arthrodesis. A biomechanical analysis

STUDY DESIGN: A comparison between femoral ring and fibular strut allografts in anterior lumbar interbody arthrodesis, as assessed by biomechanical analysis. OBJECTIVES: To assess the difference in stability and rigidity provided by the femoral ring allograft versus that provided by fibular strut allograft. SUMMARY OF BACKGROUND DATA: Two commonly used techniques for spinal arthrodesis at L4-L5 include the femoral ring allograft and the fibular strut allograft. The postoperative stability has not been evaluated biomechanically. METHODS: An anterior lumbar interbody fusion on seven cadaveric specimens was performed using femoral ring and fibular strut allografts. Biplanar radiography was used to measure the 6 degrees of motion of L4 with respect to L5 during a range of loading maneuvers. RESULTS: When an extension moment was applied, the femoral ring allograft extended 4.2 degrees more than the intact specimen, compared with 1.6 degrees with the fibular strut allograft (P = 0.18). When the flexion moment was imposed, lateral bending increased by 2.2 degrees with the femoral ring, compared with 0.7 degree with the fibular strut allograft (P = 0.06). During lateral bending, increased lateral translation was observed to be 0.9 mm with the fibular strut allograft compared with 1.4 mm with the femoral ring allograft (P = 0.06). CONCLUSIONS: Although not statistically significant, the fibular strut allograft creates a more rigid construct immediately after surgery during flexion-extension, lateral bending angulations, and lateral translation. One should consider using the fibular strut allograft over the femoral ring allograft, as it is more stable and rigid construct in the immediate postoperative period.