Effect of cage height on adjacent segment degeneration during oblique lumbar interbody fusion: a 3D finite element study

Xiao LU; Fei ZOU; Feizhou LYU; Xiaosheng MA; Xinlei XIA; Hongli WANG; Jianyuan JIANG

ABSTRACT

Objective:

To investigate the influence of interbody cage height during oblique lumbar interbody fusion (OLIF) on lumbar biomechanics with different degrees of degeneration and to provide a reference for cage choice.

Methods:

The finite element model of normal lower lumbar spine (L 3-S 1) was built and validated, then constructed three different degenerative segments in L 3, 4, and the cages with different height (8, 10,12, 14 mm) were implanted into L 4, 5 disc. All the twelve models were loaded with pure moment of 7.5 N·m to produce flexion, extension, lateral bending and axial rotation motions on lumbar spine, and the effects of cage height on range of motion (ROM), intervertebral pressure in adjacent segments and stress in facet joints were investigated.

Results:

The ROM of adjacent segments and the maximum stress of intervertebral discs increased with the increase of cage height, but this trend was not obvious in moderate and severe degeneration groups. After implantation of 4 different height cages (8, 10, 12, 14 mm), the ROM of L 3, 4 segment reached the maximum during extension. The ROM of mild degeneration group was 2.68 °, 2.71 °, 2.94 °, 2.98 °, moderate degeneration group was 2.33°, 2.37°, 2.41°, 2.49°, and severe degeneration group was 1.94 °, 1.99 °, 2.14 °, 2.21 °. The stress of L 3, 4 intervertebral disc reached the maximum during right bending. The maximum stress of L 3, 4 intervertebral disc was 23.95 MPa, 24.60 MPa, 24.90 MPa and 25.34 MPa in mild group, 25.57 MPa, 25.60 MPa, 25.82 MPa and 25.89 MPa in moderate group, and 25.95 MPa, 25.99 MPa, 26.48 MPa and 27.13 MPa in severe group. The maximum stress of L 3, 4 facet joint was 15.87 MPa, 15.78 MPa, 16.29 MPa and 16.43 MPa in mild group, 15.97 MPa, 16.31 MPa, 16.53 MPa and 16.79 MPa in moderate group, and 16.17 MPa, 16.49 MPa, 16.95 MPa and 17.35 MPa in severe group.

Conclusion:

For patients with mild lumbar degeneration requiring OLIF surgery, the intervertebral height of the surgical segment should not be overstretched. But for patients with moderate to severe lumbar degenerative disease who need to undergo OLIF surgery, it is recommended that the cage height be 0-2 mm higher than the original intervertebral space height.