Objective To analyze the correlation between the Patellotrochlear index at different knee flexion angles and recurrent patellar dislocation,and to find the optimal knee flexion angle and the best diagnostic cut-off value for predicting recurrent patellar dislocation.Methods A total of 35 patients clinically diagnosed with recurrent patellar dislocation(study group)were selected.The lengths of the central sagittal plane of the patellar cartilage and the corresponding femoral trochlear cartilage were measured at knee flexion angles ranging from 0° to 70°,in 10° increments.The Patellotrochlear index was calculated and compared with the MRI data from 55 healthy volunteers(control group).Results The Patellotrochlear index in the study group and the control group showed a positive correlation with the knee flexion angle(r=0.935 and 0.909,P＜0.001).Statistically significant differences were found between the two groups at knee flexion angles of 0°,10°,20°,30°,and 40°(t=7.480,5.742,5.200,3.558,4.271,P＜0.05).The predictive efficacy of the Patellotrochlear index for recurrent patellar dislocation varied at different knee flexion angles,with the area under the curve(AUC)and the best diagnostic cut-off values of 0.891,0.834,0.778,0.710,0.741 and 0.195,0.323,0.486,0.606,0.712,respectively.Conclusion There are significant differences in the Patellotrochlear index at different knee flexion angles.A knee flexion angle of 0° is the optimal knee flexion angle for the Patellotrochlear index to predict recurrent patellar dislocation,with a recommended best diagnostic cut-off value of 0.195.

Objective To analyze the correlation between the Patellotrochlear index at different knee flexion angles and recurrent patellar dislocation,and to find the optimal knee flexion angle and the best diagnostic cut-off value for predicting recurrent patellar dislocation.Methods A total of 35 patients clinically diagnosed with recurrent patellar dislocation(study group)were selected.The lengths of the central sagittal plane of the patellar cartilage and the corresponding femoral trochlear cartilage were measured at knee flexion angles ranging from 0° to 70°,in 10° increments.The Patellotrochlear index was calculated and compared with the MRI data from 55 healthy volunteers(control group).Results The Patellotrochlear index in the study group and the control group showed a positive correlation with the knee flexion angle(r=0.935 and 0.909,P＜0.001).Statistically significant differences were found between the two groups at knee flexion angles of 0°,10°,20°,30°,and 40°(t=7.480,5.742,5.200,3.558,4.271,P＜0.05).The predictive efficacy of the Patellotrochlear index for recurrent patellar dislocation varied at different knee flexion angles,with the area under the curve(AUC)and the best diagnostic cut-off values of 0.891,0.834,0.778,0.710,0.741 and 0.195,0.323,0.486,0.606,0.712,respectively.Conclusion There are significant differences in the Patellotrochlear index at different knee flexion angles.A knee flexion angle of 0° is the optimal knee flexion angle for the Patellotrochlear index to predict recurrent patellar dislocation,with a recommended best diagnostic cut-off value of 0.195.