Biomechanical analysis of Instrumented decompression and Interbody fusion procedures in Lumbar spine: a finite element analysis study

Interbody fusions have become increasingly popular to achieve good fusion rates. Also, unilateral instrumentation is favored to minimize soft tissue injury with limited hardware. Limited finite element studies are available in the literature to validate these clinical implications. A three-dimensional, non-linear ligamentous attachment finite element model of L3-L4 was created and validated. The intact L3-L4 model was modified to simulate procedures like laminectomy with bilateral pedicle screw Instrumentation, transforaminal, and posterior lumbar interbody fusion (TLIF and PLIF, respectively) with unilateral and bilateral pedicle screw instrumentation. Compared to instrumented laminectomy, interbody procedures showed a considerable reduction in range of motion (RoM) in extension and torsion (6% and 12% difference, respectively). Both TLIF and PLIF showed comparable RoM in all movements with < 5% difference in reduction of RoM between them. Bilateral instrumentation showed a more significant decrease in RoM (> 5% difference) in the entire range of motion except in torsion when compared to unilateral instrumentation. The maximum difference in reduction in RoM was noted in lateral bending (24% and 26% for PLIF and TLIF, respectively), while the least difference in Left torsion (0.6% and 3.6% for PLIF and TLIF, respectively) in comparing bilateral with unilateral instrumentation. Interbody fusion procedures were found to be biomechanically more stable in extension and torsion than the instrumented laminectomy. Single-level TLIF and PLIF achieved a similar reduction in RoM with a < 5% difference. Bilateral screw fixation proved biomechanically superior to unilateral fixation in the entire range of motion except in torsion.