A Hybrid Uniplanar Pedicle Screw System with a New Intermediate Screw for Minimally Invasive Spinal Fixation: A Finite Element Analysis

Table 6

Maximum von Mises stress (MPa) on the lower endplate of T12 and the upper endplate of L2 under different types of loading.

Fixation types	Stress on the lower endplate of T12				Stress on the upper endplate of L2
	Flexion	Extension	RLB	RAR	Flexion	Extension	RLB	RAR
6-MAPS	11.86	11.45	15.66	8.74	10.82	15.20	14.85	9.76
6-UPPS	11.67	11.36	16.26	9.43	10.51	15.50	15.78	10.29
6-PAPS	12.10	11.63	18.55	15.84	10.51	16.11	16.97	14.92
4-MAPS/2-NIS	11.62	11.34	15.38	8.51	10.97	15.27	14.91	9.86
4-UPPS/2-NIS	11.89	11.60	16.44	9.15	10.66	15.95	16.24	10.71
4-PAPS/2-NIS	12.06	11.67	18.16	12.89	11.65	15.65	17.25	12.33

RLB: right lateral bending; RAR: right axial rotation; 6-MAPS: six monoaxial pedicle screw fixation; 6-PAPS: six polyaxial pedicle screw fixation; 6-UPPS: six-uniplanar pedicle screw fixation; 4-MAPS/2-NIS: four monoaxial pedicle screw fixation with two new intermediate screws; 4-PAPS/2-NIS: four polyaxial pedicle screw fixation with two new intermediate screws; 4-UPPS/2-NIS: four uniplanar pedicle screw fixation with two new intermediate screws.