Basic And Clinic Study Of Neotype Shape Memory Alloy Cervical Hook For Atlantoaxial Instability

Objective(1) The biomechanical testing in vitro aimed to evaluate the stability of neotype shape memory alloy cervical hook for atlantoaxial instability, and then compare it with that of Germany AESCULAP SSE hanger technique. (2)To test the material fatigue feature of neotype shape memory alloy cervical hook for atlantoaxial instability, and then compare it with that of Germany AESCULAP SSE hanger technique. (3)To built a three-dimensional and a finite element model of atlantoaxial.(4)To study the trait of intra-stress distribution, stress vector, displacement and distortion of atlantoaxial instability during neotype shape memory alloy cervical hook was loading, in order to analyze the mechanism, security and rationality of it. To study the inner stress distribution of neotype shape memory alloy cervical hook itself. (5)To evaluate the clinical efficacy of atlantoaxial instability treatment with neotype shape memory alloy cervical hook.Methods(1)Eight fresh adult craniocervical specimens (C0-C4) used for testing the biomechanical instability were all putted into six test course. All the specimens were tested the three-dimensional ranges of motion (ROM) by Spine 2000 in the following sequence: intact, instability, Germany AESCULAP SSE hanger fixation and neotype shape memory alloy cervical hook fixation . Tested specimens were loaded with 2.0 Nm on flexion-extension, lateral bending and left and right axial rotation. Then the three-dimensional ROM of every specimen was evaluated by Geomagic Studio 5 soft package. All the specimens fixed alternately with Germany AESCULAP SSE hanger technique and neotype shape memory alloy cervical hook were loaded on MTS 858 Bionix (Material Testing System, MTS, Minneapolis, MN) with a frequency of 0.5 Hz to test their anti-fatigue characters. Statistical analysis of the data was performed using the SPSS 10.0 software package (Department of Biostatistics, FIMMU). Repeated Measures were performed to determine whether significant differences existed. (2)An intact fresh adult craniocervical specimens (C0-C3) with neotype shape memory alloy cervical hook fixed was scanned by CT with 1mm interval along its vertical axis. Then, the BMP-format data of upper-cervical were inputted into computer and reconstructed with PHILIPS system Set up a three-dimensional finite element system of upper-cervical and simulate the fixation of neotype shape memory alloy cervical hook. (3)Material property, element type and real constant refered from literature were assigned to the upper-cervical finite model which contains cervical vertebral, intervertebral discs and ligaments etc The finite element model was validated for loading force of 200N along sagittal axis or frontal axis. It can be use for evaluation the stress changes of the fixation of neotype shape memory alloy cervical hook. (4)8 patients with upper cervical instability underwent, bone grafting and internal fixation with the neotype shape memory alloy cervical hook. The patients were immobilized with soft collar for 3 months. Then seven patients were followed-up ranged from 6 months to 18 months. The NASCIS standard was adopted to evaluate the efficacy of the neotype shape memory alloy cervical hook.Results(1)According to the biomechanical testing, it showed that the flexion-extension range of motion (ROM) of atlantoaxial instability fixation with Germany AESCULAP SSE hanger fixation has no statistics difference with neotype shape memory alloy cervical hook fixation (P=0.595).The anti-fatigue characters of Germany AESCULAP SSE hanger fixation has no statistics difference with neotype shape memory alloy cervical hook fixation (P=0.239).Other group have statistics difference with each other (P＜0.05). (2)According to the biomechanical testing, it showed that the bending range of motion (ROM) of atlantoaxial instability fixation with neotype shape memory alloy cervical hook fixation has no statistics difference with intact group (P=0.053).The anti-fatigue characters of Germany AESCULAP SSE hanger fixation has no statistics difference with neotype shape memory alloy cervical hook fixation (P=0.575).Other group have statistics difference with each other (P＜0.05). (3)Biomechanical testing showed that under the rotation condition, every group has statistics difference with each other (P＜0.05). (4)A three -dimensional finite element system of upper-cervical which contains cervical vertebral, intervertebral discs, anterior longitudinal ligament, cruciate ligament and alar ligament etc was reconstructed and the fixation of neotype shape memory alloy cervical hook was simulated. (5)While loaded force of 200N along sagittal axis, the max von mises of atlantoaxial instability was 38.75 Mpa which compared with 24.49 Mpa after it fixed with neotype shape memory alloy cervical hook. While loaded force of 200N along frontal axis, the max von mises of atlantoaxial instability was 45.81 Mpa which compared with 27.46 Mpa after it fixed with neotype shape memory alloy cervical hook.(6)The results in the 7 patients followed-up visit who underwent this procedure were 4 patients with an excellent result, 3 patients with a good result. No complication was found during the following-up.Conclusion:(1)In this study, we compared the biomechanical stability of the neotype shape memory alloy cervical hook with that of intact, instability and Germany AESCULAP SSE hanger technique technique. According to the results of this in vitro study, the neotype shape memory alloy cervical hook fixation in atlantoaxial vertebrae showed an outstanding character of biomechanical stability immediately postoperative. The biomechanical rotation stability of the neotype shape memory alloy cervical hook (5.08±0.68) is higher than that of Germany AESCULAP SSE hanger fixation (8.01±1.21). The biomechanical lateral bending stability of the neotype shape memory alloy cervical hook (1.45±0.25) is lower than that of Germany AESCULAP SSE hanger fixation (0.79±0.15).(2) The anti-fatigue test of the neotype shape memory alloy cervical hook fixation showed a good character of biomechanical stability in the long-term. The biomechanical rotation stability after anti-fatigue test of the neotype shape memory alloy cervical hook (11.34±0.97) is higher than that of Germany AESCULAP SSE hanger fixation (16.20±1.00). (3)According to FEM analysis with the developed FE model, it showed that the stress values(von mises) of atlantoaxial instability was dropped after the neotype shape memory alloy cervical hook was loaded, including anterior flexion, posterior extension, lateral bending conditon., which displayed neotype shape memory alloy cervical hook fixation for the atlantoaxial instability could provide good strong fixation. (4) The self-designed memory alloy hook proves to be well designed, easy to handle with and good efficacy in posterior fixation for upper cervical instability according the clinic study.