Establishment And Biomechanical Evaluation Of The Fixation Technique For The Craniospinal Junction Cross Rod

ObjectiveFor atlantoaxial instability, rigid internal fixation is the most effective treatment method. There are numerous posterior fixation technique for craniospinal junction, posterior screw-rod produced a three-point fixation at the atlantoaxial segment and offered a best biomechanical stability, provided the highest fusion rates. The present connecting method for the craniospinal junction fixation rods consists of one rod on the left and one rod on the right, forming an approximate "II" shape frame fixation structure. In the craniospinal junction cross rod fixation technique established in this study, the two connecting rods display across-connecting "X" shape. Meanwhile, the X-shaped fixation system forms a similar fixation structure that consists of several triangles. As the triangular structure has the best stability, it may be further enhanced the stability of the structure. This study is based on the establishment and application of clinical fixation for the occipitocervical cross rod and the atlantoaxial cross rod. Different methods through the composition of different C2 screws and C1 pedicle screw, the occipital plate, respectively, on the cross fixation rod fixation method and the traditional parallel rod fixation method for biomechanical. comparison, full range of cranial ridge area at the junction of the evaluation board-rod screw system and screw-rod fixation system biomechanical stability, in order to provide theoretical support for the development of clinical application and selection.MethodsOccipital cervical fusion group:Six cervical fresh specimens were harvested to create the atlantoaxial instability model, the specimens were tested in the following order:group A1 (The occipital plate+C2 bilateral laminar screw+parallel rod), group A2 (The occipital plate+C2 bilateral laminar screw+cross rod), group B1 (The occipital plate+C2 bilateral pedicle screw+parallel rod), group B2 (The occipital plate+C2 bilateral pedicle screw+cross rod), group Cl (The occipital plate+C2 left laminar screw and right pedicle screw+parallel rod), group C2 (The occipital plate+C2 left laminar screw and right pedicle screw+cross rod), The 3D biomechanical stability of CO-2 segments was measured. Al, A2, B1, B2, Cl, C2 were compared between the two groups and compared with group N (atlantoaxial instability state CO-2 activity) respectively.Atlantoaxial fixation group:The same specimens were tested in the following order:group D1 (C1 bilateral pedicle screw +C2 bilateral laminar screw+ parallel rod), group D2 (C1 bilateral pedicle screw +C2 bilateral laminar screw+ cross rod), group El (C1 bilateral pedicle screw +C2 bilateral pedicle screw+ parallel rod), group E2 (C1 bilateral pedicle screw +C2 bilateral pedicle screw+ cross rod), group F1 (C1 bilateral pedicle screw +C2 left laminar screw and right pedicle screw+parallel rod), group F2 (C1 bilateral pedicle screw +C2 left laminar screw and right pedicle screw+cross rod), The 3D biomechanical stability of C1-2 segments was measured. Dl, D2, E1, E2, F1, F2 were compared between the two groups and compared with group M (atlantoaxial instability state C1-2 activity) respectively.ResultsOccipital cervical fusion group:In extention direction, Six fixation methods (Al, A2, B1, B2, C1, C2) had no statistical significance (P>0.05), was better than the control group N (P<0.05); In flexion direction, Six fixation methods had no statistical significance (P>0.05), was better than the control group N(P<0.05); In left lateral bending direction, Six fixation methods had no statistical significance(P>0.05), was better than the control group N (P<0.05); In right lateral bending direction, Six fixation methods had no statistical significance(P>0.05), was better than the control group N (P<0.05); In the left-hand stability, six fixation methods are better than the control group N (P<0.05). Stability of all six screw-rod fixation techniques significantly increased as compared with group A1(P<0.05). In the right-hand stability, six fixation methods are better than the control group N (P<0.05). Stability of all six screw-rod fixation techniques significantly increased as compared with A1 (P<0.05).Atlantoaxial fixation group:In the extension of stability, six fixed modes (D1, D2, E1, E2, F1, F2) were better than the control group M (P<0.05). Among them, there was no statistical significance between E2, D2, F2 and El (p>0.05). There was no statistical significance between F2、E1、F1、D1 (P>0.05), but the stability of E2 and D2 was better than D1 (P<0.05). In flexion direction, Six fixation methods had no statistical significance (P>0.05), was better than the control group M (P<0.05); In left lateral bend, ing direction, six fixation methods are better than the control group M (P<0.05). Stability of all six screw-rod fixation techniques significantly increased as compared with D1 (P<0.05). In right lateral bending direction, six fixed modes (D1, D2, El, E2, F1, F2) were better than the control group M (P<0.05). Among them, the stability of D1 was worse than E2 and El (P<0.05). In the left-hand stability, six fixation methods are better than the control group M (P<0.05). Stability of D2. E2 and F2 was better than D1、E1 and F1(P<0.05); In the right-hand stability, six fixation methods are better than the control group M (p<0.05). The stability of E2 and D2 was better than D1 (P<0.05).ConelusionNo matter the occipitocervical fixation or atlantoaxial fixation,12 fixation methods can provide sufficient biomechanical stability. In the occipitocervical fixation, cross rod can further enhance the axial rotation stabil ity of screw-rod system which was consist of occipital bone and C2 lamina screw. In atlantoaxial fixation, cross rod can further enhance the axial rotation stability of screw-rod system which was consist of C1 bilateral pedicle screws and C2 pedicle screws or C2 lamina screws. And the cross rod can further enhance the lateral stability of screw-rod system which was consist of C1 bilateral pedicle screws and C2 lamina screws.