BACKGROUND: Presently-used artificial intervertebral disk is different greatly from the normal physiological intervertebral disk in structure, material and biological properties and so on. Therefore, stress conduction at corresponding spinal section will have a certain change after the implantation of artificial intervertebral disk.OBJECTIVE: To investigate the stress distribution in small joints of normal intervertebral disk group, vertebral extirpation group and artificial lumbar intervertebral disk group with three-dimensional element method in order to discuss exploratorily the influence of the implantation of artificial lumbar intervertebral disk on the stress distribution in small joints.DESIGN: Observative and comparison experiment.SETTING: Orthopedic Department, Third Affiliated Hospital and Second Affiliated Hospital, Sun Yat-sen University; Biomechanical Laboratory in Southern Medical University.PARTICIPANTS: Spinal specimen collected from the healthy people who died in accidenct without any spinal illness (donated by their family member) was used to establish three kinds of three-dimensional element models of normal intervertebral disk, artificial intervertebral disk and vertebral extirpation as experimental subjects.METHODS: Finite element MSC.MARK software was used to establish normal intervertebral disk model with height of 10.00 mm, cross sectional area of 1300.00 mm2, and vertebral pulp cross sectional area of 495.8 mm2;in the model of vertebral pulp extirpation,the intrinsic pressure of vertebral pulp was zero; and in the three dimensional models of artificial lumbar intervertebral disk and L4-5 movement segment , the small joints were about 10.53 mm high with width of 13.37 mm and auricular area of 135 mm2.Then lumbar movement was simulated for the study of the stress distribution in small joint.MAIN OUTCOME MEASURES: Comparison of the stress in small joints under 6 kinds of states in the above three kinds of intervertebral disk movement model.RESULTS:In vertebral pulp extirpation group, the stress was proved to be the highest at superior edge, posterior middle part, lower edge and anterior middle part of small joints under anteflexion, backward extension, compression, lateroflexion and revolving states, moreover, small joint stress in artificial lumbar intervertebral disk was higher than that in normal intervertebral disk, but obviously lower than that in vertebral pulp extirpation group;however, the small joint of the middle part of artificial lumbar intervertebral disk bore the highest stress under revolving states.CONCLUSION: In contrast with vertebral pulp extirpation group, the small joint stress could be reduced after the implantant of artificial lumbar intervertebral disk, but was still higher than that of normal lumbar intervertebral disk group and the anti-verticity in artificial lumbar intervertebral disk group was markedly lower than that of normal lumbar intervertebral disk group and vertebral pulp ablation group, thus indicating that although presently-used artificial lumbar intervertebral disk possesses most of mechanical functions of normal lumbar intervertebral disk, but is still different from true lumbar intervertebral disk.

BACKGROUND: At present, there are very big differences in structure,material character and biological property between artificial intervertebral disc (AID) and normal physiological intervertebral disc.OBJECTIVE: Three-dimensional finite element method was used to observe and analysis the stress conduction of artificial lumbar intervertebral disc in lumbar motion segment.DESIGN: Single sample observation was designed.SETTING: Department of Orthopaedics, Third Affiliated Hospital, Sun Yat-sen University; Department of Orthopaedics, Second Affiliated Hospital, Sun Yat-sen University; Laboratory of Mechanics, Southern Medical UniversityPARTICIPANTS: It was to employ a vertebral sample without any spinal disorder of a healthy male died due to accidence and a finite element model of AID implantation in vertebral motion segment established with SB Charite Ⅲ AID.METHODS: According to industrial design chart of AID, finite element software MSC.MARK was utilized to establish three-dimensional model of artificial lumbar intervertebral disc. The corpus sample of motion segment of healthy lumbar vertebrae was collected and scanned with spiral CT machine and imaging documents were input in computer to preserve.Geometric model of L4-5 segment was established in three-dimensional coordinate system in ASC.MARK software. The intervertebral disc in L4-5 motion segment model was replaced by AID. It was to ensure the fixation of lower terminal lamina of L5 in the model. 4 Nm moment of force was exerted in anterior flexion, posterior extension, lateral bending and torsion on the sample successively. Finally, force of internodes representing AID was calculated and stress distribution was recorded.MAIN OUTCOME MEASURES: To observe stress distribution of anterior flexion, posterior extension, compression, lateral bending and rotation of AID.RESULTS: Finite element model of artificial lumbar intervertebral disc implanted lumbar motion segment that is in conformity with clinical practice was established. Stress distribution of AID was characterized as:er lamina was the maximum and that in the lower inclined part of slide of slide core and cover lamina was two or three times as same as that of sion, the stress in the center of slide core and cover lamina was the maximum.CONCLUSION: The finite element model of artificial lumbar intervertebral disc implanted lumbar motion segment established is in conformity with the structural character of practical artificial intervertebral disc in morphology, size and motion property, based on which, it is feasible to carry on the experiment on stress distribution of artificial intervertebral disc.

Purpose: Molecular residual disease (MRD) is a promising biomarker in colorectal cancer (CRC) for prognosis and guiding treatment, while the whole-exome sequencing (WES) based tumor-informed assay is standard for evaluating MRD based on circulating tumor DNA (ctDNA). In this study, we assessed the feasibility of a fixed-panel for evaluating MRD in CRC. Materials and Methods: Seventy-five patients with resectable stage I-III CRC were enrolled. Tumor tissues obtained by surgery, and preoperative and postoperative day 7 blood samples were collected. The ctDNA was evaluated using the tumor-agnostic and tumor-informed fixed assays, as well as the WES-based and panel-based personalized assays in randomly selected patients. Results: The tumor-informed fixed assay had a higher preoperative positive rate than the tumor-agnostic assay (73.3% vs. 57.3%). The preoperative ctDNA status failed to predict disease-free survival (DFS) in either of the fixed assays, while the tumor-informed fixed assay-determined postoperative ctDNA positivity was significantly associated with worse DFS (hazard ratio [HR], 20.74; 95% confidence interval [CI], 7.19 to 59.83; p < 0.001), which was an independent predictor by multivariable analysis (HR, 28.57; 95% CI, 7.10 to 114.9; p < 0.001). Sub-cohort analysis indicated the WES-based personalized assay had the highest preoperative positive rate (95.1%). The two personalized assays and the tumor-informed fixed assay demonstrated same results in postoperative landmark (HR, 26.34; 95% CI, 6.01 to 115.57; p < 0.001), outperforming the tumor-agnostic fixed panel (HR, 3.04; 95% CI, 0.94 to 9.89; p=0.052). Conclusion Our study confirmed the prognostic value of the ctDNA positivity at postoperative day 7 by the tumor-informed fixed panel. The tumor-informed fixed panel may be a cost-effective method to evaluate MRD, which warrants further studies in future.

Purpose: Molecular residual disease (MRD) is a promising biomarker in colorectal cancer (CRC) for prognosis and guiding treatment, while the whole-exome sequencing (WES) based tumor-informed assay is standard for evaluating MRD based on circulating tumor DNA (ctDNA). In this study, we assessed the feasibility of a fixed-panel for evaluating MRD in CRC. Materials and Methods: Seventy-five patients with resectable stage I-III CRC were enrolled. Tumor tissues obtained by surgery, and preoperative and postoperative day 7 blood samples were collected. The ctDNA was evaluated using the tumor-agnostic and tumor-informed fixed assays, as well as the WES-based and panel-based personalized assays in randomly selected patients. Results: The tumor-informed fixed assay had a higher preoperative positive rate than the tumor-agnostic assay (73.3% vs. 57.3%). The preoperative ctDNA status failed to predict disease-free survival (DFS) in either of the fixed assays, while the tumor-informed fixed assay-determined postoperative ctDNA positivity was significantly associated with worse DFS (hazard ratio [HR], 20.74; 95% confidence interval [CI], 7.19 to 59.83; p < 0.001), which was an independent predictor by multivariable analysis (HR, 28.57; 95% CI, 7.10 to 114.9; p < 0.001). Sub-cohort analysis indicated the WES-based personalized assay had the highest preoperative positive rate (95.1%). The two personalized assays and the tumor-informed fixed assay demonstrated same results in postoperative landmark (HR, 26.34; 95% CI, 6.01 to 115.57; p < 0.001), outperforming the tumor-agnostic fixed panel (HR, 3.04; 95% CI, 0.94 to 9.89; p=0.052). Conclusion Our study confirmed the prognostic value of the ctDNA positivity at postoperative day 7 by the tumor-informed fixed panel. The tumor-informed fixed panel may be a cost-effective method to evaluate MRD, which warrants further studies in future.

Purpose: Molecular residual disease (MRD) is a promising biomarker in colorectal cancer (CRC) for prognosis and guiding treatment, while the whole-exome sequencing (WES) based tumor-informed assay is standard for evaluating MRD based on circulating tumor DNA (ctDNA). In this study, we assessed the feasibility of a fixed-panel for evaluating MRD in CRC. Materials and Methods: Seventy-five patients with resectable stage I-III CRC were enrolled. Tumor tissues obtained by surgery, and preoperative and postoperative day 7 blood samples were collected. The ctDNA was evaluated using the tumor-agnostic and tumor-informed fixed assays, as well as the WES-based and panel-based personalized assays in randomly selected patients. Results: The tumor-informed fixed assay had a higher preoperative positive rate than the tumor-agnostic assay (73.3% vs. 57.3%). The preoperative ctDNA status failed to predict disease-free survival (DFS) in either of the fixed assays, while the tumor-informed fixed assay-determined postoperative ctDNA positivity was significantly associated with worse DFS (hazard ratio [HR], 20.74; 95% confidence interval [CI], 7.19 to 59.83; p < 0.001), which was an independent predictor by multivariable analysis (HR, 28.57; 95% CI, 7.10 to 114.9; p < 0.001). Sub-cohort analysis indicated the WES-based personalized assay had the highest preoperative positive rate (95.1%). The two personalized assays and the tumor-informed fixed assay demonstrated same results in postoperative landmark (HR, 26.34; 95% CI, 6.01 to 115.57; p < 0.001), outperforming the tumor-agnostic fixed panel (HR, 3.04; 95% CI, 0.94 to 9.89; p=0.052). Conclusion Our study confirmed the prognostic value of the ctDNA positivity at postoperative day 7 by the tumor-informed fixed panel. The tumor-informed fixed panel may be a cost-effective method to evaluate MRD, which warrants further studies in future.

Purpose: Molecular residual disease (MRD) is a promising biomarker in colorectal cancer (CRC) for prognosis and guiding treatment, while the whole-exome sequencing (WES) based tumor-informed assay is standard for evaluating MRD based on circulating tumor DNA (ctDNA). In this study, we assessed the feasibility of a fixed-panel for evaluating MRD in CRC. Materials and Methods: Seventy-five patients with resectable stage I-III CRC were enrolled. Tumor tissues obtained by surgery, and preoperative and postoperative day 7 blood samples were collected. The ctDNA was evaluated using the tumor-agnostic and tumor-informed fixed assays, as well as the WES-based and panel-based personalized assays in randomly selected patients. Results: The tumor-informed fixed assay had a higher preoperative positive rate than the tumor-agnostic assay (73.3% vs. 57.3%). The preoperative ctDNA status failed to predict disease-free survival (DFS) in either of the fixed assays, while the tumor-informed fixed assay-determined postoperative ctDNA positivity was significantly associated with worse DFS (hazard ratio [HR], 20.74; 95% confidence interval [CI], 7.19 to 59.83; p < 0.001), which was an independent predictor by multivariable analysis (HR, 28.57; 95% CI, 7.10 to 114.9; p < 0.001). Sub-cohort analysis indicated the WES-based personalized assay had the highest preoperative positive rate (95.1%). The two personalized assays and the tumor-informed fixed assay demonstrated same results in postoperative landmark (HR, 26.34; 95% CI, 6.01 to 115.57; p < 0.001), outperforming the tumor-agnostic fixed panel (HR, 3.04; 95% CI, 0.94 to 9.89; p=0.052). Conclusion Our study confirmed the prognostic value of the ctDNA positivity at postoperative day 7 by the tumor-informed fixed panel. The tumor-informed fixed panel may be a cost-effective method to evaluate MRD, which warrants further studies in future.