Biomechanical Impact of Titanium Cage Tilt in the Sagittal Plane in Lumbar Total Spondylectomy: a Finite Element...

To study the biomechanical effects of tilting titanium cages on internal fixation devices in TES surgery.

We used finite element analysis to simulate lumbar total en bloc spondylectomy (TES). Five models were constructed: (a) the intact model (L1-S); (b) the TES model after L3 removal; and the TES model with a titanium cage tilted at (c) 5°, (d) 10°, or (e) 15° in the sagittal plane. The sacrum was fixed to simulate the stress during lumbar flexion, extension, lateral bending to the left and right, and rotation to the left and right, and measured the biomechanical response of the internal fixation system.

The range of motion (ROM) in segments L1-5 of the TES surgical model was significantly reduced compared to the intact model, with a decrease of 66.87-96.49%. The maximum von Mises stress (VMS) in the pedicle screw system occurred during left lateral bending, reaching 283.9 MPa, while the minimum VMS occurred during flexion, at 114.7 MPa; during rotation, the maximum endplate stress was observed at L2 and L4, with values of 30.8 MPa and 22.7 MPa, respectively. When comparing the tilted cage models c-e to the neutral cage model b , the ROM of the lumbar spine most notably increased during left and right rotations, with an increase of 166.5%-227.6%. The VMS in the pedicle screw-rod system significantly increased during rotation, with a peak value of 421.3 MPa, and the VMS in the titanium cage also showed a marked increase, with a maximum value of 733.5 MPa. The VMS of the lower endplate at L2 increased to a range of 21.6 MPa to 113.0 MPa, and the VMS of the upper endplate at L4 increased to a range of 12.0 MPa to 66.9 MPa.

After the titanium cage is tilted, the pedicle screw-rod system, the titanium cage, and the upper and lower endplates of the adjacent vertebrae all experience an increase in stress. This stress elevation is most critical during rotational movements. Although the stress values fluctuated across different tilt angles (5°, 10°, 15°), no consistent dose-response relationship was observed in this model. This suggests that the presence of sagittal tilt itself may be a more critical factor influencing stress than the exact degree of tilt within the 5°-15° range.