Biomechanical study of posterior flexible and dynamic fixations in the occipitocervical region

doi:10.13418/j.issn.1001-165x.2022.3.13

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Chinese Journal of Clinical Anatomy ›› 2022, Vol. 40 ›› Issue (3) : 315-319. DOI: 10.13418/j.issn.1001-165x.2022.3.13

Biomechanical study of posterior flexible and dynamic fixations in the occipitocervical region

Tong Jie1,2, Ji Wei1, Huang Zhiping1, Zhou Ruozhou1,2, Fang Zuozhong2, Zhu Qingan1*

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Abstract

Objective To analyze the effects of flexible and dynamic fixation on the stability of the occipitocervical region. Methods Biomechanical tests were performed by using six fresh adult cervical spines (occipital bone-C4 segment, Oc~C4), with the fixation site extended from the occipital bone to the C3 vertebra. The following conditions were stimulated: (1) Intact state; (2) Injury state: a combination of type II odontoid fractures and atlanto-occipital capsule injury; (3)Rigid fixation: a 3.5 mm diameter titanium rod was used to connect C3 lateral mass screws, C1, and C2 were fixed with common pedicle screws; (4) Flexible fixation: a 2.0 mm diameter titanium rod was used to fix Oc~C3 with locking connections between the screws and rods; (5) Fixation by using two rotating pedicle screws; (6) C1 and C2 were fixed with four rotating pedicle screws; (7) C1, C2 and C3 were fixed with six rotating pedicle screws. Biomechanical studies were performed by using a spinal testing machine, while applying a constant moment of 1.5 Nm in flexion-extension, left-right lateral bending, and left-right axial rotation directions were measured to analyze the range of motion (ROM) and neutral zone (NZ) of Oc~C3 segments. Results ROM of 2.0mm diameter rod fixation was significantly larger than that of rigid fixation in all directions (P<0.05). Compared with the rigid fixation, ROM of Oc~C3 in C1 and C2with a fixation that used 2~4 rotating pedicle screws was similar in all directions (P>0.05). The application of six rotating pedicle screws in C1~C3 significantly increased ROM for rotation in Oc~C3 with statistical significance (P=0.031). Different fixation methods significantly reduced the neutral zone of fixed segment in flexion, extension, lateral bending and rotation directions (P<0.05). Conclusions In the occipital cervical region Oc~C3, the stability of all directions with using flexible fixation was weaker than that of rigid fixation. In the occipital cervical region, the stability of using two or four rotating screw fixations in C1 and C2 is similar to that of rigid fixation. Using six rotating screw fixations is as stable as rigid fixation in directions of flexion, extension and lateral bending, but weaker in the direction of rotation.

Key words

Atlas; / / Axis; / Occipital cervical region; / Flexible fixation； / Dynamic fixation; / / Stability; / / Biomechanics

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Tong Jie, Ji Wei, Huang Zhiping, Zhou Ruozhou, Fang Zuozhong, Zhu Qingan. Biomechanical study of posterior flexible and dynamic fixations in the occipitocervical region[J]. Chinese Journal of Clinical Anatomy. 2022, 40(3): 315-319 https://doi.org/10.13418/j.issn.1001-165x.2022.3.13

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