The influence of bilateral pedicle screw fixation on vibration response of the disc degenerated human lumbar spine: A finite element stress analysis

BACKGROUND: Very few studies have evaluated biomechanical characteristics of the disc degenerated human lumbar spine after bilateral pedicle screw fixation (BPSF) under whole body vibration (WBV) that is typically present in vehicles. OBJECTIVE: To examine the influence of BPSF on stress responses of the disc degenerated human lumbar spine to WBV using finite element (FE) method. METHODS: Two previously validated Ll-S1 FE models with different grades of disc degeneration (mild and moderate) at L4-L5 were employed, and the two degenerated models were instrumented with bilateral pedicle screws and rods across the L4-L5 level, respectively. Transit dynamic analyses were performed on all these models under a 400 N compressive follower preload and a 40 N sinusoidal vertical vibration load. Intradiscal pressure (IDP) and von Mises stress (VMS) of the annulus ground substance in all disc levels of the degenerated models and the corresponding implanted models were recorded and compared. RESULTS: BPSF decreased maximum response values and vibration amplitudes of the IDP and annulus VMS in both the degenerated and adjacent levels of the lumbar spine. CONCLUSIONS: Application of the BPSF system is helpful in prevention of further injury of the disc degenerated lumbar spine during WBV.