Bicortical Screw Purchase at Upper Instrumented Vertebra (UIV) Can Cause UIV Fracture After Adult Spinal Deformity Surgery: A Finite Element Analysis Study

Abstract

Objective: To examine the biomechanical stress distribution at the upper instrumented vertebra (UIV) according to unicortical-and bicortical purchase model by finite element analysis (FEA). Methods: A T8 to Sacrum with implant finite element model was developed and validated. The pedicle screws were unicortically or bicortically inserted from T10 to L5, and each model was compared and the von Mises (VM) yield stress of T10 was calculated. According to the motion (flexion, extension, lateral bending, and axial rotation) of spine, boundary condition values were set as 15°, 15°, 10°, 4°. Results: Although the 2 stress values did not show a significant difference between the unicortical-and bicortical purchase models in the flexion and extension, bicortical purchase model showed a larger stress distribution. However, the asymmetric behavior was significantly greater in the case of lateral bending (0.802 MPa vs. 0.489 MPa) and the rotation (5.545 MPa vs. 4.905 MPa). The greater stress was observed on the spinal body surface abutting the implanted screw. Although the maximum stress was observed around the implanted screw in the bicortical purchase model under axial loading, the VM stress of both models was not significantly different. Conclusion: Bicortical purchase model showed a larger stress distribution than the unicortical model, especially in the case of lateral bending and the rotation behavior. Our biomechanical simulation by FEA indicates that bicortical fixation at UIV can be a risk factor for early UIV compression fracture after adult spinal deformity surgery.

Surgical Impact on Global Sagittal Alignment and Health-Related Quality of Life Following Cervical Kyphosis Correction Surgery: Systematic Review

“…4 In primary thoracolumbar deformities, the loss of lumbar lordosis (LL) is accompanied by an increased pelvic tilt (PT), cervical hyperlordosis, hip extension, knee flexion, and ankle dorsiflexion. 5 Similarly, primary cervical deformities contribute to thoracolumbar deformities and spinopelvic imbalance. 2,6 Cervical sagittal imbalance causes significant impairment due to the inability to gaze horizontally and is associated with poorer health-related quality of life (HRQoL) and functional disability.…”

“…These changes occur not only through mobile spine segments, but also pelvis and the lower extremities [ 4 ]. In primary thoracolumbar deformities, the loss of lumbar lordosis (LL) is accompanied by an increased pelvic tilt (PT), cervical hyperlordosis, hip extension, knee flexion, and ankle dorsiflexion [ 5 ]. Similarly, primary cervical deformities contribute to thoracolumbar deformities and spinopelvic imbalance [ 2 , 6 ].…”

Surgical Outcomes and Complications Following All Posterior Approach for Spinal Deformity Associated with Neurofibromatosis Type-1

“…In the case No. 1 patient, there were no the occurrence of proximal junctional kyphosis or proximal junctional failure after surgery 8,18,33) (Fig. 4).…”

The Incidence of Adding-On or Distal Junctional Kyphosis in Adolescent Idiopathic Scoliosis Treated by Anterior Spinal Fusion to L3 Was Significantly Higher Than by Posterior Spinal Fusion to L3

“…[11][12][13] The previously reported factors or criteria are valuable to determine distal fusion levels in AIS. 1,2,10,13,14 However, absolute guidelines for the selection of LIV have not been defined. In the current study, we found several key risk factors for AO or DJK.…”