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

Study Design. A comparison between femoral ring and fibular strut allograft s in anterior lumbar interbody arthrodesis, as assessed by biomechanical an alysis. 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 arthrod esis at L4-L5 include the femoral ring allograft and the fibular strut allo graft. The postoperative stability has not been evaluated biomechanically. Methods. An anterior lumbar interbody fusion on seven cadaveric specimens w as performed using femoral ring and fibular strut allografts. Biplanar radi ography was used to measure the 6 degrees of motion of L4 with respect to L 5 during a range of loading maneuvers. Results. When an extension moment was applied, the femoral ring allograft e xtended 4.2 degrees more than the intact specimen, compared with 1.6 degree s 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, co mpared with 0.7 degrees with the fibular strut allograft (P = 0.06). During lateral bending, increased lateral translation was observed to be 0.9 mm w ith 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 allo graft creates a more rigid construct immediately after surgery during flexi on-extension, lateral bending angulations, and lateral translation. One sho uld consider using the fibular strut allograft over the femoral ring allogr aft, as it is a more stable and rigid construct in the immediate postoperat ive period.