BACKGROUND:Vertebral compression fracture is a common disease in the current orthopedic field.However,the occurrence of re-fracture in neighboring vertebrae after surgery is a problem that cannot be ignored,which has a serious impact on the normal life of patients. OBJECTIVE:The aim of this study is to establish four postoperative models with different recovery heights using computed tomography images.By using finite element analysis,we derived the stresses on the neighboring vertebrae at different recovery heights and further explored the importance of postoperative recovery of the height of the injured vertebrae. METHODS:A finite element model of the thoracolumbar spine(T11-L3)was established and validated,on the basis of which four postoperative finite element models of L1 with different recovery heights of 100%,80%,60%,and 40%were constructed,in which the cement capacity varied with the recovery height.The specific models are as follows:Model 1 was the postoperative model with normal recovery height,and the cement capacity was 8.3 mL.Model 2 was the postoperative model in which 20%of the anterior height of the L1 was removed and the posterior convexity angle became 10.41°,and the cement capacity was 6.9 mL.Model 3 was the postoperative model in which 40%of the anterior height of the L1 was removed and the posterior convexity angle became 20.17°,and the cement capacity was 4.7 mL.Model 4 was a postoperative model with 60%of the L1 anterior height removed and the posterior convexity angle changed to 28.85°,with a cement capacity of 3.6 mL.For evaluation of the postoperative model,we applied a moment of 7 Nm and an axial force of 500 N.The followings were recorded and analyzed:peak stresses in the L2 upper endplate and T12 lower endplate;peak stresses in the L2 and T12 cancellous bone. RESULTS AND CONCLUSION:(1)The highest peak stresses for each condition of the L2 upper endplate,T12 lower endplate,L2 cancellous bone,and T12 cancellous bone occurred in Model 1 and Model 4.In particular,the T12 lower endplate,except for the posterior extension condition,the anterior flexion,left and right lateral bending,and left and right rotation conditions all reached their highest peak stresses in Model 4,with stresses of 50.3,33.1,44.9,34.3,and 31.9 MPa.(2)Based on the peak stresses in the adjacent vertebral endplates and cancellous bone,after excluding Model 1 and Model 4,the minimum peak stresses for most of the conditions appeared in the Model 2,and the minimum peak stresses appeared in the Model 2 in 66.6%of the cases,especially in the upper endplates of the L2 and cancellous bone except for the posterior extension condition,the minimum peak stresses all appeared on the Model 2.(3)Therefore,controlling the recovery height at about 100%and 40%of the original height was a dangerous recovery height,which had a greater impact on the neighboring vertebrae.Controlling the recovery height at about 80%of the original height may be a more ideal choice.With a recovery height of about 80%of the original height,the adjacent vertebrae are subjected to less stress,thus reducing the risk of re-fracture of the adjacent vertebrae in the patient.

BACKGROUND:The elastic modulus of traditional bone implants is large and does not match the elastic modulus of human bone,which will cause a stress shielding effect and lead to bone resorption.The trabecular scaffold of the triply periodic minimal surface with radial gradient has elastic modulus matching with human cancellous bone,and its yield strength is greater than that of human cortical bone,which provides a new choice for the design of bone scaffold. OBJECTIVE:Triply periodic minimal surface structure with radial gradient was constructed by the implicit surface method.The sample was manufactured by laser selective melting technology,and the quasi-static compression test was carried out to obtain trabecular scaffolds with mechanical properties matching human bones. METHODS:Four types of the trabecular scaffolds of the triply periodic minimal surface with a radial gradient of G,I,P and D were established by the implicit surface method.Samples were manufactured by laser selective melting technology.We observed the surface morphology of the molded sample,evaluated the molding quality,conducted a quasi-static compression test,and evaluated the mechanical properties of the samples. RESULTS AND CONCLUSION:The quasi-static compression test results showed that compared with the four triply periodic minimal surface scaffolds,the platform stress of the G scaffold had less fluctuation and no failure or fracture,indicating that the G scaffold had the best plasticity.The mechanical properties of the G scaffolds with 45%,55%and 65%porosities were analyzed.It was found that the elastic modulus of G scaffolds with 55%porosity was within the range of elastic modulus of human cancellous bone(0.022-3.7 GPa),and the yield strength was close to the maximum yield strength of human cortical bone(187.7-222.3 MPa).In conclusion,G triply periodic minimal surface scaffold with 55%porosity can reduce the stress shielding effect,bear a higher body load,improve the stability of the implant,and prolong the service life of the implant.

Objective:To explore the application value of the method of judging the density of small shadows in the lung area by using CT and CT reference films for pneumoconiosis.Methods:The chest imaging data of 244 employees of a large copper company in Tongling City, Anhui Province who underwent occupational physical examination at Tongling Municipal Hospital in Anhui Province from January 2016 to December 2019 were retrospectively analyzed. Totally 244 cases underwent chest CT scan and chest DR radiography at the same time. The shape and size of the small shadows (the size of the circular and quasi-circular nodules in the lung area were represented by p, q, r, and the size of the irregular small shadows were represented by s, t, u), the overall density, the density of small shadows in each lung area, the large shadows, and the diagnosis stage were observed and compared. The small shadow density of each lung area was judged by the method of judging the small shadow density of CT lung area and the reference film, and other observation indicators were judged according to GBZ70-2015 Diagnosis of Occupational Pneumoconiosis. Results:There was a significant difference between CT and DR in judging s-shaped small shadows and no small shadows ( P<0.05), and there was no statistically significant difference in judging p, q, r, t, and u-shaped small shadows ( P>0.05). CT and DR had medium to high consistency in the judgment of the overall density of small shadows (Kappa=0.692, P=0.001), and the diagnostic coincidence rate was 82.38% (201/244). There was moderate to high agreement between CT and DR in the density of small shadows shown in the right upper, right lower, left upper, left middle, and left lower lung regions (Kappa ranged from 0.40 to 0.75, P<0.05), and the consistency in the right middle lung region was poor (Kappa=0.381, P=0.001). Eleven large shadows were detected in 8 cases by DR, 31 large shadows were detected in 23 cases by CT, and 20 (8.20%) large shadows were detected more frequently by CT than DR. The agreement between CT and DR for the diagnosis and staging of silicosis was excellent (Kappa=0.843, P=0.001), and the diagnostic coincidence rate was 91.80% (224/244). Conclusion:Applying the method of determining the density of small shadows in the lung area of pneumoconiosis and reference films, combined with GBZ70-2015 Diagnosis of Occupational Pneumoconiosis, can make a more accurate diagnosis of silicosis.