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Objective To compare the biomechanical effects of contiguous three-level cervical Hybrid surgery[anterior cervical discectomy and fusion (ACDF) + cervical disc arthroplasty ( CDA)] and three-level ACDF. Methods The finite element model of C1-T1 cervical-thoracic spine was developed based on CT data. Three models were simulated by the implantation of Prestige LP and Zero-P prostheses, including two Hybrid models (AFA, Prestige LP implanted at C3-4 and C5-6 segments and Zero-P implanted at C4-5 segment; FAF, Zero-P implanted at C3-4 and C5-6 segments and Prestige LP implanted at C4-5 segment) and three-level ACDF model(FFF). The changes in range of motion (ROM) of adjacent levels during flexion, extension, lateral bending and axial rotation, the overall ROM, as well as the intradiscal pressure ( IDP) and facet contact force ( FCF) of adjacent levels were compared. Results The ROM in adjacent levels and the overall ROM of the AFA modelwere closer to the intact model, and the maximum increases in the ROM of the adjacent levels for the FAF and FFF models were 15. 0% and 23. 4% , respectively. For AFA, FAF and FFF models, the maximum increases in the maximum IDP of adjacent levels were 19. 0% , 66. 7% , 147. 6% , and the maximum increases in FCF were 17. 4% , 55. 7% , 80. 1% , respectively. Conclusions This study provides biomechanical basis for three-level cervical Hybrid surgery in treating patients with the contiguous three-level cervical degenerative disc disease.
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Objective To analyze biomechanical properties of cervical spine after anterior cervical discectomy and fusion (ACDF) and total disc replacement (TDR) surgery. Methods Twelve cadaveric cervical spines (C2-T1) were adopted, and the motion and load distributions of the cervical segments under intact state and after ACDF and TDR surgery were tested using a three-dimensional (3D) optoelectronics measurement system. All the tests were carried out with displacement control in directions of flexion (Flex), extension (Ext), left bending (LB), right bending (RB), left rotation (LR) and right rotation (RR). Motion characteristics of the normal cervical spine and the implant were also discussed. Results In TDR-treated specimens, range of motion (ROM) was well preserved and could restore to the normal ROM distributions, especially in Flex/Ext and LR/RR direction. While in ACDF-treated specimens, ROM presented a large decrease as much as to 73.41% under the same condition compared with TDR, and ROM distributions were also changed obviously in other motions for the segments. Significant changes of ROM in LB/RB direction occurred in both TDR and ACDF group, which were up to 45.92% and 108.06%, respectively. The experimental data indicated that the normal motion of cervical spines was a 3D coupled motion, especially in LB/RB direction, where a 35% rotation around X-axis existed. The cervical spine could recover close to normal coupled motion after TDR surgery. Conclusions TDR surgery can restore the physiological motion of cervical spines more close to the normal state, especially in Flex/Ext and LR/RR direction. The study provides a theoretical basis and quantitative reference for TDR and ACDF surgery in clinic.
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OBJECTIVE: We describe a surgical tool that uses the distractor pin as a reference for determining proper screw length in ACDF. It is critical that screw purchase depth be as deep as possible without violating or penetrating the posterior cortical wall, which ensures strong pull out strength. METHODS: We enrolled 81 adult patients who underwent ACDF using an anterior cervical plate from 2010 to 2012. Patients were categorized into Groups A (42 patients: retractor pin used as a reference for screw length) and B (39 patients: control group). Intraoperative lateral x-rays were taken after screwing the retractor pin to confirm the approaching vertebral level. The ratio of retractor pin length to body anteroposterior (A-P) diameter was measured as a reference. Proper screw length was determined by comparison to the reference. RESULTS: The average distance from screw tip to posterior wall was 3.0+/-1.4mm in Group A and 4.1+/-2.3mm in Group B. The ratio of screw length to body sagittal diameter was 86.2+/-5.7% in Group A and 80.8+/-9.0% in Group B. Screw length to body sagittal diameter ratios higher than 4/5 occurred in 33 patients (90%) in Group A and 23 patients (59%) in Group B. No cases violated the posterior cortical wall. CONCLUSION: We introduce a useful surgical method for determining proper screw length in ACDF using the ratio of retractor pin length to body A-P diameter as a reference. This method allows for deeper screw purchase depth without violation of the posterior cortical wall.