| Objective: A biomechanical experiment was conducted by encapsulating the Fiber Bragg Grating(FBG)in a pre-grooved steel plate and using optical measurement instruments and methods,together with orthopedic biomechanical laboratory instruments,to measure the changes in stress indirectly through measuring the changes in the reflectance spectrum.A preliminary study was performed to test the measuring method using FBG encapsulation on steel plate and its application prospects in the measurement of steel plate biomechanical stress changes in the Department of Orthopedic Trauma,as well as to determine the form of FBG encapsulation on steel plate and the pattern of its position during stress changes.This preliminary study served to propel further research on the application of FBG in clinical practice,and to provide objective reference for the firmness of the fixation on the fractured ends of the bone,postoperative functional exercise guidance and the assessment of final fracture healing.Methods: Middle transverse fracture was made on 10 fresh sheep tibias with grinded ends(Fig 2),and were numbered 1-10.Slots(0.5mm depth x0.5mm width)were made on the front and side of ten 8-hole upper limb fixation steel plates(Shandong Weigao,upper-limb long bone internal fixation plate),followed by the encapsulation of FBG inside the two slots.The 10FBG-encapsulated steel plates were numbered 1-10,and were fixed onto the corresponding 1-10 sheep tibia fractures.Three pieces of self-tapping internal fixation screws(3.5mm×18mm and 3.5mm×20mm)were drilled into the distal and proximal ends of the fracture,at 1mm away from the opposite side of the tibia steel plate.A total of 10 experimental models were prepared.(1)One end of the encapsulated FBG on the side of the steel plate was connected to the single input port on a 1x2 coupler,and the spectrometer(EDFA)and spectrumanalyzer(AO6317B)were connected to the other two ports on the coupler(Fig 1)respectively.The experimental model was then placed onto the biomechanics machine,and vertical pressure was applied at an increment of10±5N to test its vertical compression.The biomechanical load,displacement and wavelength changes measured by the spectrum analyzer were recorded.(2).The three point bending test was performed using the biomechanical machine.Bending pressure was applied at three points on the model with an increment of 7±3N,and the biomechanical load,displacement and wavelength changes measured by spectrum analyzer were recorded.(3).The encapsulated FBG on the front of the steel plate was connected with the spectrometer and spectrum analyzer.The experimental model was then placed onto the biomechanics machine,and vertical compression was applied at an increment of 10±5N.The biomechanical load,displacement and wavelength changes measured by the spectrum analyzer were recorded.(4).The three point bend test was performed on the FBG on the front steel plate.Pressure was applied at three points on the model using the biomechanics machine at an increment of about 7 ±3N,and biomechanical load,displacement and wavelength changes measured by the spectrum analyzer were recorded.The above four steps were repeated for other 9 groups,and the load,displacement and wavelength changes in each group were recorded.(5)A model was randomly selected to repeat the above tests in turn for 5 times to carry out intra-group testing,and the load,displacement and wavelength changes of each round of testing were recorded.Finally,the 10 models were installed in a three point bending state for destructive testing,and the wavelength changes following the increase in load were recorded.The significance of this test was to determine the maximum steel plate deformation and displacement,and the corresponding load data measured by the optical fiber.Results:1 Inter-group statistical analysis: the normality test was conducted on the data of each group.It was found that the vertical compression and three point bending data measured by the front encapsulated FBG were normallydistributed in each group,while those measured by the side FBG were not normally distributed.(1)Displacement in the 10 model groups was increased as the load increased during the four steps mention above.the process;(2)Bivariate correlation analysis of the load and wavelength data recorded by the side FBG during vertical compression showed P>0.05 in all 10 groups,suggesting that there was no linear correlation between vertical load and wavelength measured by the side FBG;(3)Bivariate correlation analysis of the load and wavelength data recorded by the side FBG during three point bending showed P>0.05 in all 10 groups,suggesting that there was no linear correlation between bending load and wavelength measured by the side FBG;(4)Bivariate correlation analysis of the load and wavelength data recorded by the front FBG during vertical compression showed P<0.05 in all 10 groups,suggesting that there was a linear correlation between vertical load and wavelength measured by the front FBG;(5)Bivariate correlation analysis of the load and wavelength data recorded by the front FBG during three point bending showed P<0.05 in all 10 groups,suggesting that there was a linear correlation between bending load and wavelength measured by the front FBG.2 Intra-group statistical analysis: Statistical analysis was performed on the data recorded by the selected group.The data from each round of testing were subjected to the normality test.It was found that the 5 sets of vertical compression and three point bending data measured by the front encapsulated FBG were normally distributed,while those measured by the side FBG were not normally distributed.Bivariate correlation analysis of the 5 sets of load and wavelength data recorded by the front FBG during vertical compression all showed P<0.05,suggesting that there was a linear correlation between vertical load and wavelength measured by the front FBG.Bivariate correlation analysis of the 5 sets of load and wavelength data recorded by the front FBG during three point bending all showed P<0.05,suggesting that there was a linear correlation between bending load and wavelength measured by the front FBG.In contrast,bivariate correlation analysis of the 5 sets of load and wavelength data recorded by the side FBG during vertical compression allshowed P>0.05,suggesting that there was no linear correlation between vertical load and wavelength measured by the side FBG.Bivariate correlation analysis of the 5 sets of load and wavelength data recorded by the side FBG during three point bending all showed P<0.05,suggesting that there was no linear correlation between bending load and wavelength measured by the side FBG.3 Three point destructive bending of the 10 model groups showed that the values of the reflection center wavelength recorded on the spectrum analyzer began to fluctuate when the test load in each group was increased to600-650 N.Conclusion:1 It is feasible to use FBG to measure biomechanics data in the Department of Orthopedic Trauma,as it can record the changes in wavelength resulted from steel plate displacement under different loads.It is also possible to encapsulate FBG on a steel plate to measure the deformation and displacement of the steel plate due to load-induced displacement of the ends of the bone following plate fixation of long bone fractures.2 Different form and position of FBG encapsulation greatly influence the wavelength changes measured by the spectrum analyzer.3 Regardless of vertical compression or bending,FBG encapsulated at the front of the steel plate is able to show good linear correlation between the measured wavelength and the load.However,FBG encapsulated at the side of the steel plate showed no linear correlation between the measured wavelength and vertical compression or bending.Regardless of vertical compression or bending within the same group,the side FBG shows no linear correlation between the measured wavelength and load,while the front FBG shows a linear correlation between the two.4 The statistical results were consistent between intra-group and inter-group analyses.The steel plate itself has no effect on the measurement results,and the model has great reproducibility.5 Wavelength data begin to fluctuate when the load reaches 600-650 N onthe biomechanics machine,indicating that the internal structure of the fiber is damaged,and the increase in load has reached the fiber’s limit of detection.6 This study demonstrated that the wavelength measured by the FBG encapsulated at the front of the steel plate has extremely strong linear correlation with the load.Based on this finding,further series of studies and mathematical model conversions can be performed to measure the displacement changes in the fractured ends of the bone under different loads,and thereby provide objective reference for the firmness of the fixation on the fractured ends of the bone,postoperative functional exercise guidance and the assessment of final fracture healing. |
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