Biomechanical analysis of lumbar nonfusion dynamic stabilization using a pedicle screw-based dynamic stabilizer or an interspinous process spacer

This study aimed to investigate and compare the effects of two widely used nonfusion posterior dynamic stabilization (NPDS) devices, pedicle screw-based dynamic stabilizer (PSDS) and interspinous process spacer (IPS), on biomechanics of the implanted lumbar spine under static and vibration loadings. The finite element model of healthy human lumbosacral segment was modified to incorporate NPDS device insertion at L4-L5 segment. Bioflex and DIAM were used as PSDS-based and IPS-based NPDS devices, respectively. As a comparison, lumbar interbody fusion with rigid stabilization was also simulated at L4-L5. For static loading, segmental range of motion (ROM) of the models under moments of four physiological motions was computed using hybrid testing protocol. For vibration loading, resonant modes and dynamic stress of the models under vertical excitation were extracted through random response analysis. The results showed that compared with the rigid fusion model, ROM of the nonfusion models was higher at L4-L5 level but lower at adjacent levels (L1- L2, L2-L3, L3-L4, L5-S1). Compared with the Bioflex model, the DIAM model produced higher ROM at L4-L5 level but lower ROM at adjacent levels, especially under lateral bending and axial rotation; resonant frequency of the DIAM model was slightly lower; dynamic response of nucleus stress at L4-L5 level was slightly higher for the DIAM model, and the dynamic stress at adjacent levels was no obvious difference between the nonfusion models. This study reveals biomechanical differences between the Bioflex and DIAM systems, which may provide references for selecting surgical approaches in clinical practice.