Biomechanical Evaluation of the Cross‐link Usage and Position in the Single and Multiple Segment Posterior Lumbar Interbody Fusion

OBJECTIVE: Previous studies have neither explored the usage of cross‐links nor investigated the optimal position of the cross‐links in posterior lumbar interbody fusion (PLIF). This study evaluates biomechanical properties of cross‐links in terms of different fixation segments and optimal position in single‐ and multi‐segment posterior lumbar interbody fusion. METHODS: Two finite element (FE) models of instrumented lumbosacral spine with single‐(L4/5) and multi‐segment (L3‐S1) PLIF surgery were simulated. On the basis of the two models, the benefits of the usage of cross‐links were assessed and compared with the status of no application of cross‐links. Moreover, the effects of position of cross‐links on multi‐segment PLIF surgery were studied in Upper, Middle, and Lower positions. RESULTS: No significant difference was found in the range of motion (ROM), intersegmental rotational angle (IRA) of adjacent segments, and intradiscal pressure (IDP) regardless of the usage of cross‐links in the single‐segment PLIF surgery, while the cross‐link increased the maximum von Mises stress in the fixation (MSF) under the axial rotation (53.65 MPa vs 41.42 MPa). In the multi‐segment PLIF surgery, the usage of cross‐links showed anti‐rotational advantages indicated by ROM (Without Cross‐link 2.35(o), Upper, 2.24(o); Middle, 2.26(o); Lower, 2.30(o)) and IRA (Without Cross‐link 1.19(o), Upper, 1.08(o); Middle, 1.09(o); Lower, 1.13(o)). The greatest values of MSF were found in without cross‐link case under the flexion, lateral bending, and axial rotation (37.48, 62.61, and 86.73 MPa). The application of cross‐links at the Middle and Lower positions had lower values of MSF (48.79 and 69.62 MPa) under the lateral bending and axial rotation, respectively. CONCLUSION: The application of cross‐links was not beneficial for the single‐segment PLIF, while it was found highly advantageous for the multi‐segment PLIF. Moreover, the usage of cross‐links at the Middle or Lower positions resulted in a better biomechanical stability.