| Part Ⅰ Finite Element Study on the Treatment of Unstable Atlas fracture with Posterior Osteosynthesis Using a New Self-designed Lateral Mass Screw-plate SystemObjective:To establish and verify the three-dimensional finite element model of the normal upper cervical spine.On this basis,to establish the atlas fracture model and internal fixation model,to verify the reduction feasibility of the new self-designed lateral mass screw-plate system,and to evaluate the mechanical properties of the new screw-plate system by finite element analysis.Methods:A healthy male volunteer was selected and his upper cervical spine(C0-C2)was scanned by thin-slice CT after signing the corresponding informed consent letter.After data were obtained,the bone model was constructed by three-dimensional reconstruction method.After importing the finite element modeling software,the finite element model of normal C0-C2 upper cervical spine was obtained.The range of motion under flexion,extension,curvature and rotation conditions was measured,and the validity of the model was verified by comparing with previous literature data.After the model was established,the classic Jefferson four-part fracture instability model was established on this basis and the range of motion under different working conditions was obtained.After loading the new self-designed lateral mass screw-plate system,the three-dimensional motion and screw-plate stress nephogram were obtained by using the finite element analysis software again,and the biological stability of the new lateral mass screw-plate system and the stress characteristics of the screw-plate under different working conditions were analyzed and evaluated.Results:The range of motion of C0-C1 and C1-C2 in the fracture model(C0-C1:6.3°,27.2°,7.5°,11.9°;C1-C2:12.3°,13.6°,9.5°,51.1°)was significantly greater than that in the normal model(C0-C1:4.0°,22.6°,5.9°,7.5°;C1-C2:9.8°,10.5°,3.9°,37.3°)under flexion,extension,curve and rotation.The range of motion of C0-C1 increased by 57.50%,20.35%,27.12%and 58.67%,respectively.C1-C2 range of motion increased by 25.51%,29.52%,143.59%and 37.00%,respectively.The range of motion of C0-C1 and C1-C2 in the internal fixation model(C0-C1:4.1°,22.6°,5.9°,7.5°;C1-C2:10.2°,11.0°,4.1°,38.5°)was almost the same as that in the normal model,but slightly increased in the internal fixation model.C0-C1 range of motion increased by 2.50%,2.21%,1.69%and 4.00%,and C1-C2 range of motion increased by 4.08%,4.76%,5.13%and 3.22%,respectively.The stress nephogram of internal fixation model under different working conditions indicated that the stress of internal fixation under physiological activities was in an acceptable range,mainly located at the junction of screw and plate,and there was no obvious stress concentration.Conclusions:The upper cervical spine(C0-C2)finite element analysis model created in this study is representative,and the data obtained based on this model is highly accurate.The results of finite element analysis indicate that the new self-designed lateral mass screw-plate system is scientifically designed and has high feasibility without obvious stress concentration.The new self-designed lateral mass screw-plate system has high three-dimensional stability and retains the motor function of the occipito-atlantoaxial joint.Part Ⅱ Biomechanical Study on the Treatment of Unstable Atlas fracture with Posterior Osteosynthesis Using a New Self-designed Lateral Mass Screw-plate SystemObjective:To establish the normal model group,the atlas fracture model group and the internal fixation model group,and to measure the three-dimensional range of motion(ROM),stiffness value and fatigue test of the cervical spine on the above models by biomechanical test,so as to evaluate the effect of the activity retention and stability of the new self-designed lateral mass screw-plate system,and to provide the basis for clinical application.Methods:Eight fresh human cadaveric specimens of occipito-neck spine were selected,and a normal model group was made after the inclusion of bone fracture,deformity,severe degeneration and osteoporosis were excluded.The three-dimensional range of motion(ROM)and stiffness of the upper cervical spine were measured by biomechanical test system under the state of forward flexion/extension,left/right curvature and left/right rotation.The classic Jefferson four-part fracture instability model was constructed by disconnecting the anterior and posterior arches and transverse ligaments of the model.The three-dimensional range of motion(ROM)and stiffness values were measured.Finally,the new self-designed lateral mass screw-plate system was fixed on the fracture model group to simulate the fracture reduction process,and the three-dimensional range of motion(ROM)and stiffness values were measured again.After 2000 cycles of flexion and extension,lateral bending and rotation fatigue tests,the three-dimensional range of motion(ROM)of the internal fixation model group was measured again and compared with that before the fatigue test to evaluate the stability of internal fixation.Results:C0-C1 and C1-C2 three-dimensional range of motion(ROM):① The ROM values of the fracture model group(C0-C1:20.34 ± 1.56°/21.21 ± 2.10°,14.69 ± 0.68°/15.01 ±0.97°,25.64 ± 0.89° 24.69 ± 1.12°;C1-C2:19.76 ± 1.46° 18.99 ± 1.86°,13.21 ± 1.65°/12.89 ± 1.35°,39.43 ± 0.97°/37.64 ± 2.35°)and the normal model group(C0-C1:12.20±1.10°/11.98±0.97°,7.68±0.56°/7.23±0.64°,13.96±0.93°/13.21±1.12°;C1-C2:10.65 ± 1.10°/10.43 ± 0.65°,6.74 ± 1.69° 7.01 ± 1.54°,22.33 ± 2.02°/23.44± 1.85°)were significantly different in the six directions of flexion/extension,left/right curve and left/right rotation(P<0.05),and the ROM value of fracture model group was significantly higher than that of normal group;② Compared with the normal model group,the ROM values in the six directions of flexion/extension,left/right bending and left/right rotation were slightly increased in the internal fixation model group(C0-C1:13.10± 0.96° 12.21 ± 1.15°,8.16 ± 1.63° 7.74 ± 1.74°,14.21 ± 1.54° 13.99± 1.32°;C1-C2:10.99 ± 1.55° 10.91 ± 0.76°,7.01 ± 1.31° 7.33 ± 0.64°,22.64 ± 1.15°/23.84 ± 1.84°),but the difference was not statistically significant(P>0.05).③Compared with the fracture model group,the ROM values in the six directions of flexion/extension,left/right curve and left/right rotation decreased in the internal fixation model group,and the differences were statistically significant(P<0.05).Stiffness values:①Flexion,extension,lateral bending and torsional stiffness of fracture model group(1.18 ± 0.17 N ·CM/deg,1.21 ± 0.19 N ·CM/deg,2.01 ± 0.18 N·CM/deg,1.09 ± 0.21 N ·CM/deg)decreased significantly compared with normal model group(1.84 ± 0.21 N ·CM/deg,1.87 ± 0.24N ·CM/deg,3.05 ± 0.17N ·CM/deg,1.91 ± 0.13 N ·CM/deg),and the difference was statistically significant(P<0.05);②Flexion,extension,lateral bending and torsional stiffness of the internal fixation model group(1.79 ± 0.18N ·CM/deg,1.81 ± 0.20N ·CM/deg,2.98 ± 0.21 N ·CM/deg,1.88 ± 0.14 N ·CM/deg)were slightly decreased compared with the normal model group,but the difference was not statistically significant(P>0.05).③ The flexion,extension,lateral bending and torsional stiffness of the internal fixation model group were significantly increased compared with the fracture model group,and the difference was statistically significant(P<0.05).Fatigue test:The range of C0-C1 and C1-C2 after the fatigue test(C0-C1:14.06 ± 0.64° 13.11 ± 1.32°,9.01 ± 1.69° 8.39 ± 1.84°,14.82± 0.81° 14.51± 1.23°;C1-C2:11.65±0.78° 11.55± 1.11°,7.82± 1.36°/8.05 ± 1.49°,23.14 ± 1.89°/24.30 ± 0.97°)in the internal fixation group was slightly larger than that before the fatigue test(C0-C1:13.10 ± 0.96°/12.21 ± 1.15°,8.16 ±1.63° 7.74 ± 1.74°,14.21 ± 1.54° 13.99 ± 1.32°;C1-C2:10.99 ± 1.55° 10.91 ± 0.76°,7.01 ± 1.31°/7.33 ± 0.64°,22.64 ± 1.15°/23.84 ± 1.84°)in terms of forward bending/backward extension,left/right bending and left/right rotation,but the difference was not statistically significant(P>0.05).Conclusion:The new self-designed lateral mass screw-plate system can effectively reduce and restore the stability of the unstable atlas fracture through simple posterior surgery,while preserving the normal range of motion of the upper cervical spine without restricting the movement of the upper cervical spine.The biomechanical results of this study are excellent,but there are still some defects,and the long-term efficacy needs further clinical verification.Part Ⅲ Preliminary Clinical Study on the Treatment of Unstable Atlas Fracture with Posterior Osteosynthesis Using a New Self-designed Lateral Mass Screw-plate SystemObjective:In the treatment of unstable atlas fractures using the combined anterior-posterior approach or the posterior monoaxial screw-rod system,factors such as severe trauma or complex surgical procedures still need to be improved despite the favourable reduction effect.The article described and evaluated a new technique for the treatment of unstable atlas fracture using a self-designed lateral mass screw-plate system.Methods:A total of 10 patients with unstable atlas fractures using this new screw-plate system from January 2019 to December 2021 were retrospectively reviewed.All patients underwent posterior open reduction and internal fixation(ORIF)with a self-designed screw-plate system.The medical records and radiographs before and after surgery were noted.Preoperative and postoperative CT scans were used to determine the type of fracture and evaluate the reduction and union of fracture.Results:All 10 patients were successfully operated with this new system,with an average follow-up of 16.7 ± 9.6 months.A total of 10 plates were placed,and all 20 screws were inserted into the atlas lateral masses.The mean duration of the procedure was 108.7 ±20.1 minutes and the average estimated blood loss was 98.0 ± 41.3 ml.The lateral mass displacement(LMD)averaged 7.1 ± 1.9 mm before surgery and almost achieved satisfactory reduction after surgery.All the fractures achieved bony healing without reduction loss or implant failure.No complications(vertebral artery injury,neurologic deficit,or wound infection)occurred in these 10 patients.At the final follow-up,the anterior atlantodens interval(AADI)was 2.3 ± 0.8 mm and the visual analog scale(VAS)was 0.6 ± 0.7 on average.All patients achieved a well-preserved range of motion of the upper cervical spine and a good clinical outcome at the final follow-up.Conclusions:Posterior osteosynthesis with this new screw-plate system can provide a new therapeutic strategy for unstable atlas fractures with simple and almost satisfactory reduction. |
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