Biomechanics of implant failure after PSO: Influence of the hardware configuration through a finite element analysis

Abstract

Pedicle Subtraction Osteotomy (PSO) is a technique for restoring the correct sagittal balance that achieves corrections up to 35°. The procedure still shows a high rate of complications (10–25%, usually rod breakage at the osteotomy level): in order to decrease this rate a computational comparative analysis investigating the effects of a set of variables on the instrumentation has been set up. In particular the number of rods, the material, the diameter, and the presence of an anterior support have been considered in an FE model of L1-S1 simulating a PSO at either L3 or L4. Standing was simulated using a follower load of 500 N and pure moments of ± 7.5 Nm in flexion, extension, lateral bending, and axial rotation evaluating the load sharing between the anterior part of the spine and the rods and the stress in the rods. Analyzing our results we can suggest the use of a multiple rod configuration, associated with the use of an anterior support in order to reduce the stresses on the instrumentation.