Carl-Eric Aubin1, Marco Cammarata2, Xiaoyu Wang3, Jean-Marc Mac-Thiong4. 1. Department of Mechanical Engineering, Polytechnique Montréal, PO Box 6079, Downtown Station, Montreal, Quebec H3C 3A7, Canada; Sainte-Justine University Hospital Center, 3175 Cote Sainte-Catherine Road, Montreal, Quebec H3T 1C5, Canada. Electronic address: carl-eric.aubin@polymtl.ca. 2. Department of Mechanical Engineering, Polytechnique Montréal, PO Box 6079, Downtown Station, Montreal, Quebec H3C 3A7, Canada; Hôpital du Sacré-Cœur de Montréal, 5400 Boulevard Gouin West, Montreal, Quebec H4J 1C5, Canada. 3. Department of Mechanical Engineering, Polytechnique Montréal, PO Box 6079, Downtown Station, Montreal, Quebec H3C 3A7, Canada; Sainte-Justine University Hospital Center, 3175 Cote Sainte-Catherine Road, Montreal, Quebec H3T 1C5, Canada. 4. Sainte-Justine University Hospital Center, 3175 Cote Sainte-Catherine Road, Montreal, Quebec H3T 1C5, Canada; Hôpital du Sacré-Cœur de Montréal, 5400 Boulevard Gouin West, Montreal, Quebec H4J 1C5, Canada.
Abstract
STUDY DESIGN: Biomechanical analysis of proximal junctional kyphosis (PJK) through numerical simulations. OBJECTIVES: Assessment of the effect of sagittal alignment, the upper instrumented vertebral level (UIV), and 4 other surgical variables on biomechanical indices related to the PJK risks. SUMMARY OF BACKGROUND DATA: Despite retrospective clinical studies, biomechanical analysis of individual parameters associated with PJK is lacking to support instrumentation strategies to reduce the PJK risks. METHODS: Instrumentations of 6 adult scoliosis cases with different operative strategies were simulated (1,152 simulations). Proximal junctional (PJ) angle and flexion loads were evaluated against the sagittal alignment and the proximal instrumentation level. RESULTS: Instrumenting 1 more proximal vertebra allowed the PJ angle, proximal moment, and force to be reduced by 18%, 25%, and 16%, respectively. Shifting sagittal alignment by 20 mm posteriorly increased the PJ angle and proximal moment by 16% and 22%, and increased the equivalent posterior extensor force by 37%. Bilateral complete facetectomy, posterior ligaments resection, and the combination of the 2 resulted in an increase of the PJ angle (by 10%, 28%, and 53%, respectively), flexion forces (by 4%, 12%, and 22%, respectively), and proximal moments (by 16%, 44%, and 83%, respectively). Transverse process hooks at UIV compared with pedicle screws allowed 26% lower PJ angle and flexion loads. The use of proximal transition rods with proximal diameter reduced from 5.5 to 4 mm slightly reduced PJ angle, flexion force, and moment (less than 8%). The increase in sagittal rod curvature from 10° to 40° increased the PJ angle (from 6% to 19%), flexion force (from 3% to 10%), and moment (from 9% to 27%). CONCLUSIONS: Simulated posteriorly shifted sagittal alignment was associated with higher PJK risks, whereas extending instrumentation proximally allowed a lower mechanical risk of PJK. Preserving PJ intervertebral elements and using a more flexible anchorage at UIV help reduce the biomechanical risks of PJK.
STUDY DESIGN: Biomechanical analysis of proximal junctional kyphosis (PJK) through numerical simulations. OBJECTIVES: Assessment of the effect of sagittal alignment, the upper instrumented vertebral level (UIV), and 4 other surgical variables on biomechanical indices related to the PJK risks. SUMMARY OF BACKGROUND DATA: Despite retrospective clinical studies, biomechanical analysis of individual parameters associated with PJK is lacking to support instrumentation strategies to reduce the PJK risks. METHODS: Instrumentations of 6 adult scoliosis cases with different operative strategies were simulated (1,152 simulations). Proximal junctional (PJ) angle and flexion loads were evaluated against the sagittal alignment and the proximal instrumentation level. RESULTS: Instrumenting 1 more proximal vertebra allowed the PJ angle, proximal moment, and force to be reduced by 18%, 25%, and 16%, respectively. Shifting sagittal alignment by 20 mm posteriorly increased the PJ angle and proximal moment by 16% and 22%, and increased the equivalent posterior extensor force by 37%. Bilateral complete facetectomy, posterior ligaments resection, and the combination of the 2 resulted in an increase of the PJ angle (by 10%, 28%, and 53%, respectively), flexion forces (by 4%, 12%, and 22%, respectively), and proximal moments (by 16%, 44%, and 83%, respectively). Transverse process hooks at UIV compared with pedicle screws allowed 26% lower PJ angle and flexion loads. The use of proximal transition rods with proximal diameter reduced from 5.5 to 4 mm slightly reduced PJ angle, flexion force, and moment (less than 8%). The increase in sagittal rod curvature from 10° to 40° increased the PJ angle (from 6% to 19%), flexion force (from 3% to 10%), and moment (from 9% to 27%). CONCLUSIONS: Simulated posteriorly shifted sagittal alignment was associated with higher PJK risks, whereas extending instrumentation proximally allowed a lower mechanical risk of PJK. Preserving PJ intervertebral elements and using a more flexible anchorage at UIV help reduce the biomechanical risks of PJK.