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@#AIM: To compare the difference of biomechanical stability after a femtosecond laser-assisted <i>in situ</i> keratomileusis(FS-LASIK)and laser-assisted subepithelial keratomileusis(LASEK)by ocular response analyzer(ORA). <p>METHODS: This prospective study was conducted at the First Affiliated Hospital of Harbin Medical University, and myopic patients with the equivalent sphere between -2.00 and -5.00 diopters from January 2016 and December 2017 were enrolled. All the subjects were divided into FS-LASIK and LASEK group respectively according to different surgical methods. There were 64 patients(100 eyes)participated in the FS-LASIK group while 53 patients(100 eyes)in the LASEK surgery group. Corneal hysteresis value(CH)and corneal resistance factor value(CRF)were measured pre-, 1mo and 3mo postoperation of all the subjects. And the variance analysis of two groups was repeated to compare the overall difference between the two modes of operation from pre-operation to post operation. <p>RESULTS: The CH and CRF value of the two groups were different before and after operation(<i>P</i><0.05). The comparison results of repeated measurements showed that the CH value and CRF value of the surgical methods were reduced in 1 and 3mo after operation, respectively, and there was significance(<i>P</i><0.05). The CH and CRF of FS-LASIK group was lower than LASEK group only in 1mo after the operation(<i>P</i><0.05). <p>CONCLUSION: Both surgeries could affect the biomechanical stability of cornea. From the point of view of biomechanical stability, LASEK operation is safer than FS-LASIK operation and reduces the possibility of postoperative refractive regression.
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PURPOSE: This study using the finite element analysis (FEA) focused on evaluating the biomechanical stability of the LC-DCP in accordance with existing of the fracture gap at the facture site after bone fracture augmentation. MATERIALS AND METHODS: For FEM analysis, total eleven types with different fracture models considering clinical fracture cases were constructed according to the fracture gap sizes (0, 1, 4 mm)/widths (0, 25, 50, 75, 100%). Limited contact dynamic compression plate (LC-DCP) fixation system was used in this FEM analysis, and three types of load were applied to the bone-plate fixation system: compressive, torsional, bending load. RESULTS: The results in FEM analysis showed that the 1, 4 mm fracture gap sizes and 75% or more fracture gap widths increased considerably the peak von Mises stress (PVMS) both the plate and the screw under all loading conditions. PVMS were concentrated on the center of the LC-DCP bone-plate, and around the necks of screws. CONCLUSION: Based on the our findings, we recommend at least 50% contact of the fracture faces in a fracture surgery using the compression bone-plate system. Moreover, if x-ray observation after surgery finds 100% fracture gap or 50% or more fracture gap width, supplementary measures to improve biomechanical stability must be taken, such as restriction of walking of the patient or plastering.
Subject(s)
Humans , Finite Element Analysis , Fractures, Bone , Neck , WalkingABSTRACT
PURPOSE: The goal of this study using the biomechanical test was to evaluate the mechanical stability of the bone-plate fixation system according to changes of the fracture gap sizes and widths. MATERIALS AND METHODS: For mechanical test, four types with different fracture models simulating the clinical situations were constructed depending on the gap size (FGS, mm) and the gap width (FGW, %) at the fracture site: 0 mm/0%, 1 mm/100%, 4 mm/100%, 4 mm/50%. For analyzing the effects of fracture gap on the biomechanical stability of the bone-plate fixation system, 4-point bending test was performed under all same conditions. RESULTS: It was found that the fracture gap sizes of 1 and 4 mm decreased mechanical stiffness by about 50~60% or more. Furthermore, even without fracture gap size, 50% or more fracture gap width considerably decreased mechanical stiffness and suggested the possibility of plate damage through strain results. CONCLUSION: Our findings suggested that at least 50% contact of the fracture faces in a fracture surgery would be maintained to increase the mechanical stability of the bone-plate fixation system.
Subject(s)
Fractures, Bone , Sprains and StrainsABSTRACT
[Objective]To explore the biomechanical stability of fixation with two and three cannulated compression screws in treatment of the adductive femoral neck fractures by the three-dimensional finite element analysis(FEA).[Method]Two FEA models of two screws and three screws for adductive femoral neck facture fixations were set up to investigate the simulated loading of three different conditions.[Result]At the condition of the heel touching the ground and the middle position,there was no difference in the biomechanical stabilities of the two models.However,at the condition of the tiptoe departing from the groud,the model of three screws fixation was better in torsion resistance and stretching resistance.[Conclusion]The biomechanical stability of fixation with two screws is determined by the direction of loading.Three cannulated compression screws fixation provides better biomechanical stability.
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[Objective] To evaluate the biomechanical stability of lumbar intact specimen,anterior lumbar interbody fixation(ALIF)specimen,ALIF specimen fixed with pedicle screw and ALIF specimen fixed with translaminar facets screw.[Method]Each of eight adult fresh cadaver specimen of lumbarsacral segmcnts was analyzed in four states(groups):intact,L5S1 ALIF,L5S1 ALIF fixed with pedicle screw or fixed with translaminar facets screw,test and compare its range of motion(ROM)in flexion,extension,lateral bending and axial rotation.[Result]The ROM of ALIF specimen in extension was larger than that of intact specimen(P
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PURPOSE: To analyze the effects of implant design on the primary stability and the contact between bone and prosthesis of three different porous coated acetabular implants. MATERIALS AND METHODS: The distal part of sixty bovine femurs were employed. 52 mm acetabular cups were inserted tightly after 2mm under-reaming. Trilogy acetabular cups were inserted in Group I, Mallory head finned RingLoc cups in Group II, Duraloc spiked cups in Group III. The gaps between the acetabular cups and the bones were measured on the radiography. The axial compression test and rotation test were performed using Instron. RESULTS: The gaps between the acetabular cup and bone of Gorup I and II was significantly smaller than Group III at its central adjacent and peripheral area (p0.05) . The mean torque of 1 degree rotation test was higher in the Group III than in the group I and II without statistical significance (p>0.05) . The mean torque of 2, 3 and 5 degree rotation test was highest in Group II among three, but there were no statistical differences among three groups (p>0.05) . CONCLUSION: Triology and Mallory-Head cup can be assumed to have better primary stability than Duraloc cup. And additional fin or spikes attached on the acetabular implant couldn't enhance the primary bone-prosthesis interface stability.