A Biomechanical Analysis on the Influence of Variable Thoracolumbar Correction on Proximal Junctional Kyphosis

Study DesignCadaveric Biomechanical Study.ObjectivesSurgical treatment for adult spinal degeneration revolves around posterior instrumented fusion. Proximal junctional kyphosis (PJK) is a well-documented complication of this surgical treatment and theorized to occur due to excessive mobility at the proximal non-fused segments. The goal of this study was to identify whether increasing rod correction into greater lordosis correlates with a higher degree of mobility at proximal spinal levels.MethodsSeven, native cadaveric human spines (T9-sacrum) were instrumented with bilateral pedicle screws posteriorly from T12 to sacrum. Native spines were maneuvered to determine the sagittal plane intervertebral range of motion (ROM). The spines were then instrumented with rods three times to achieve increasing levels of lordotic correction, and the same ROM tests were conducted. Flexion-Extension (FE) torque and adjacent level intervertebral flexion/extension rotations were measured.ResultsSignificant decreases in Cobb Angle between corrections were measured. Max Flexion Torque increased significantly with increasing correction. The proximal spinal levels saw increased Max Flexion ROM and decreased Max Extension ROM as a function of correction. The FE ROM of the proximal spinal levels increased compared to the Native condition but sequentially decreased slightly with increased correction.ConclusionsThis study indicates that, while increasing lordotic correction does not increase total proximal spinal mobility, it does change its distribution. This segmental motion distribution change implies that additional flexion mobility is introduced to adjacent spinal levels as a correction increased. Future work will explore how to better quantify risk factors intraoperatively for increased adjacent segment mobility to better prevent PJK.