Biomechanical Analysis of Proximal Junctional Kyphosis in Osteoporotic Thoracolumbar Fusion With Different Reinforcement Strategies

The biomechanics of proximal junctional kyphosis (PJK) in osteoporotic thoracolumbar fusion patients require further exploration, particularly regarding the efficacy of different strengthening strategies such as vertebral augmentation (VA) and ligament tethers (TE). The effects of three strengthening strategies: double-segment VA (T7&T8VA), three-level posterior TE (T6-T9TE), and combination of VA with TE (VATE) were compared in osteoporotic patients using a thoracolumbar T1-L5 finite element model to assess the impact on mechanical transfer to proximal vertebrae, intervertebral disc stress, and loads on the pedicle screw system. The ratios of maximum von Mises stress at the T7 in the posterior thoracolumbar fusion (PTCF), T7&T8VA, T6-T9TE, and VATE models were 1:0.87:0.75:0.64, 1:0.98:0.35:0.33, 1:0.96:0.89:0.86, and 1:0.99:0.97:0.95 for the mild osteoporotic models during flexion, extension, lateral bending, and axial rotation, respectively. Compared with the PTCF model, T7/T8 IVD maximum stresses in T7&T8VA, T6-T9TE, and VATE models were decreased by 7.08%, −0.38%, 4.42%, −0.67%; 27.7%, 72.72%, 8.97%, 0.17%; and 34.51%, 73.61%, 12.57%, −0.36% under identical conditions. The stresses at SCR8 in T7&T8VA, T6-T9TE, and VATE increased over the PTCF model by 2.66%, 8.23%, 1.80% and 1.26%, 1.64%, 2.72% during flexion and rotation, respectively, and decreased by 3.40%, 32.92%, 34.06% and 4.61%, 7.37%, 11.07% during extension and lateral bending, respectively. In both mild and severe osteoporotic models, the strengthening methods of T7&T8VA, T6-T9TE, and VATE exhibited similar trends of changes, but the stress values were significantly higher in the latter. The combination of T7&T8VA with T6-T9TE is more effective in preventing PJK after posterior long-segment T8-L5 fusion surgery than using T7&T8VA alone or T6-T9TE alone for osteoporotic patients. Simulation results can provide theoretical foundations and assist surgeons in selecting the appropriate operation scheme to prevent PJK for osteoporotic patients.