Biomechanical effects of posterior lumbar interbody fusion with vertical placement of pedicle screws compared to traditional placement

Table 1 Material property settings

Material name	Elastic modulus (MPa)	Poisson's ratio
Trabecular bone	200	0.2
Cortical bone	12000	0.3
Pedicle screw	3500	0.25
Intervertebral disc	3.4	0.39
Screw-rod system	120000	0.33

Table 2 Pull-out strength of pedicle screws (unit: N)

TSA	Pull-out resistance	Maximum vertebral stress
0 degrees	132.8 ± 4.99	2.0058 ± 0.0031
7 degrees	139.6 ± 5.24	2.001 ± 0.0029
10 degrees	145.4 ± 6.09	2.0015 ± 0.0058
17 degrees	149.8 ± 6.72	2.0066 ± 0.0075
F	314.683	1.928
P value	0.001	0.182

TSA: Transverse section angle.

Table 3 Maximum stress calculations for pedicle screws (unit: MPa)

TSA	Extension	Flexion	Right lateral bending	Left lateral bending	Right rotation	Left rotation
0 degrees	437.85 ± 11.72	335.1 ± 9.85	433.64 ± 10.15	612.31 ± 22.52	657.5 ± 44.84	582.2 ± 47.57
17 degrees	626.18 ± 44.45	242.8 ± 21.52	648.5 ± 83.31	488.62 ± 36.67	551.12 ± 24.01	548.4 ± 46.03
F	1313.129	196.715	1875.31	546.879	3557.963	1261.657
P value	0.000	0.000	0.000	0.000	0.000	0.000

TSA: Transverse section angle.

Table 4 Load-displacement ratio for pedicle screws (unit: N/mm)

TSA	Extension	Flexion	Right lateral bending	Left lateral bending	Right rotation	Left rotation
0 degrees	2740.93 ± 165.32	392.80 ± 22.71	483.01 ± 29.98	394.84 ± 20.03	351.67 ± 20.84	396.13 ± 23.69
17 degrees	2165.44 ± 131.12	353.29 ± 20.36	527.13 ± 33.77	425.08 ± 24.35	364.43 ± 19.14	428.47 ± 27.76
F	124.963	33.72	72.107	6.14	4.986	7.093
P value	0.000	0.000	0.000	0.011	0.028	0.001

TSA: Transverse section angle.

Table 5 Maximum stress in the vertebral body (unit: MPa)

TSA	Extension	Flexion	Right lateral bending	Left lateral bending	Right rotation	Left rotation
0 degrees	68.585 ± 4.41	77.245 ± 5.21	69.775 ± 4.19	78.91 ± 6.05	72.192 ± 4.22	68.45 ± 4.09
17 degrees	39.079 ± 2.40	55.681 ± 3.89	65.348 ± 4.09	72.734 ± 5.02	66.227 ± 4.31	45.756 ± 3.19
F	628.454	197.455	78.021	48.819	14.763	368.721
P value	0.000	0.000	0.000	0.000	0.000	0.000

TSA: Transverse section angle.

Table 6 Vertebral load displacement ratio (unit: N/mm)

TSA	Extension	Flexion	Right lateral bending	Left lateral bending	Right rotation	Left rotation
0 degrees	1827.29 ± 114.78	261.87 ± 16.01	318.39 ± 20.71	307.10 ± 21.09	273.52 ± 18.13	264.10 ± 17.33
17 degrees	1443.65 ± 83.75	274.79 ± 18.53	344.18 ± 27.18	327.74 ± 23.35	283.45 ± 17.06	281.93 ± 21.99
F	134.605	6.144	229.409	97.584	3.775	8.134
P value	0.000	0.012	0.000	0.000	0.027	0.001

TSA: Transverse section angle.