Objective:To investigate the correlation between the set mechanical angle(MA)by using an auxiliary photography device and the actual knee flexion angle(FA)in axial X-ray imaging for patellofemoral joint,so as to provide a theoretical basis for applying a self-developed dynamic adjustment device to achieve precisely dynamic radiography for patellofemoral joint,and to optimize diagnostic protocols of imaging for patellar dislocation,subluxation,etc..Methods:A prospective experimental design was adopted,which enrolled 96 healthy volunteers(40 males,56 females)whose age was 18-65 years old(mean age:32.6 years old).Using a self-developed dynamically auxiliary radiography device for axial position of patellofemoral joint,and the MA was set at 90°,120°,135°,150°,and 160°,and the corresponding FA was measured.At the same time,the gender,age,body mass index(BMI),thigh circumference,and calf circumference were also recorded.Statistical analysis was performed using SPSS 25.0 software.One-sample t-test was applied to analyze the difference value between MA and FA(MA-FA).Pearson correlation analysis and multiple linear regression analysis were conducted to conduct correlation analysis for the distribution characteristics of FA under different MA values,the FA and each anthropometric indicator.Results:FA showed a linear relationship with MA,BMI,thigh circumference,calf circumference,and gender.The regression equation was:FA=62.031+0.511×MA+0.489×BMI+0.189×thigh circumference-0.445×calf circumference+4.67×gender(R2=0.82,P<0.001).When MA was set at 90°,The actual FA was(112.21±4.7)° that was significantly larger than MA(90°),and the difference was significant(t=46.26,P<0.001).When MA was set at 120°,the actual FA was(126.19±6.43°),which was significantly greater than MA(120°)(t=9.42,P<0.001).When MA was set at 135°,there was not significant difference between FA and MA(P>0.05).When MA was set at 150°,the actual FA was(141.44±4.42°)that was significantly smaller than MA(150°),and the difference was significant(t=-18.97,P<0.001).When MA was set at 160°,the actual FA was(148.55±5.33°)that was significantly smaller than MA(160°),and the difference was significant(t=-21.03,P<0.001).BMI,thigh circumference,and calf circumference were the main factors of influencing the difference between MA and FA.Conclusion:Using the self-developed dynamic auxiliary radiography device for axial position of patellofemoral joint can construct a mathematical model to accurately predict,regulate and control the knee flexion angle,which can realize standardization for dynamic radiography on patellofemoral joint,and has significant clinical value in improving the diagnostic accuracy for imaging of patellar dislocation and subluxation.

Objective:To investigate the correlation between the set mechanical angle(MA)by using an auxiliary photography device and the actual knee flexion angle(FA)in axial X-ray imaging for patellofemoral joint,so as to provide a theoretical basis for applying a self-developed dynamic adjustment device to achieve precisely dynamic radiography for patellofemoral joint,and to optimize diagnostic protocols of imaging for patellar dislocation,subluxation,etc..Methods:A prospective experimental design was adopted,which enrolled 96 healthy volunteers(40 males,56 females)whose age was 18-65 years old(mean age:32.6 years old).Using a self-developed dynamically auxiliary radiography device for axial position of patellofemoral joint,and the MA was set at 90°,120°,135°,150°,and 160°,and the corresponding FA was measured.At the same time,the gender,age,body mass index(BMI),thigh circumference,and calf circumference were also recorded.Statistical analysis was performed using SPSS 25.0 software.One-sample t-test was applied to analyze the difference value between MA and FA(MA-FA).Pearson correlation analysis and multiple linear regression analysis were conducted to conduct correlation analysis for the distribution characteristics of FA under different MA values,the FA and each anthropometric indicator.Results:FA showed a linear relationship with MA,BMI,thigh circumference,calf circumference,and gender.The regression equation was:FA=62.031+0.511×MA+0.489×BMI+0.189×thigh circumference-0.445×calf circumference+4.67×gender(R2=0.82,P<0.001).When MA was set at 90°,The actual FA was(112.21±4.7)° that was significantly larger than MA(90°),and the difference was significant(t=46.26,P<0.001).When MA was set at 120°,the actual FA was(126.19±6.43°),which was significantly greater than MA(120°)(t=9.42,P<0.001).When MA was set at 135°,there was not significant difference between FA and MA(P>0.05).When MA was set at 150°,the actual FA was(141.44±4.42°)that was significantly smaller than MA(150°),and the difference was significant(t=-18.97,P<0.001).When MA was set at 160°,the actual FA was(148.55±5.33°)that was significantly smaller than MA(160°),and the difference was significant(t=-21.03,P<0.001).BMI,thigh circumference,and calf circumference were the main factors of influencing the difference between MA and FA.Conclusion:Using the self-developed dynamic auxiliary radiography device for axial position of patellofemoral joint can construct a mathematical model to accurately predict,regulate and control the knee flexion angle,which can realize standardization for dynamic radiography on patellofemoral joint,and has significant clinical value in improving the diagnostic accuracy for imaging of patellar dislocation and subluxation.