P1. How important is the anterior column support in a long lumbopelvic spinal fixation? An in-silico biomechanics analysis

Abstract

BACKGROUND CONTEXT The addition of anterior column support at the bottom of a long construct has been proposed to support the lumbosacral junction and potentially prevent posterior lumbopelvic fixation failure. However, a retrospective study has shown that adding anterior column support is not sensitive to construct failure, highlighting the possibility that posterior fusion quality may be a more important factor than previously thought. PURPOSE To determine the role of biological tissue support via posterolateral gutters or anterior column support in off-loading traditional posterior thoracolumbopelvic instrumented fusion in patients who have experienced rod failure versus non-failure patients. STUDY DESIGN/SETTING Finite element analysis. PATIENT SAMPLE N/A OUTCOME MEASURES N/A METHODS Finite element models (T10-Pelvis) were created to match the average spinal-pelvic parameters of two cohorts of patients reported in the literature, major-failure (defined as pseudarthrosis or rod fracture above S1) and non-failure groups. A load was applied at the T10 superior endplate to simulate gravimetric loading in a standing position. Posterior solid fusion was simulated by applying spring elements attached to the adjacent vertebrae. Anterior column support was simulated by assigning cancellous bone properties to the L4-S1 disc. RESULTS Upper body weight acting on the long-instrumented spine resulted in 18% higher translation, 14% higher rotation and 20% higher stress in the major failure group than in the non-failure group. Solid posterior fusion decreased translation and rotation, and also alleviated rod stress in the lower lumbar region. In this case, anterior support did not change the stress pattern. Conversely, simulated pseudarthrosis produced stress patterns similar to those of the construct-only spine. In this case, adding anterior support dramatically alleviated stress at the index levels. CONCLUSIONS The spinopelvic parameters of the major-failure group produced increased gravity load, resulting in increased stresses in comparison to the non-failure group. Simulated posterior fusion in the lumbar region helped reduce stresses in both major failure and non-failure patients. However, in cases with a simulated pseudarthrosis, rod stresses were amplified by major failure spinal alignment. In this case, anterior column support was a major factor in reducing rod stress, and should be considered for patients with poor alignment. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.