[Diagnostic value of Blumensaat angle for anterior cruciate ligament injury]

The receiver operator characteristic(ROC) curve was used to determine the best Blumensaat angle for the diagnosis of anterior cruciate ligament injury, so as to objectively evaluate the diagnostic value of Blumensaat angle for anterior cruciate ligament injury.

Total 167 patients who had knee arthroscopic treatment in a hospital from January 2015 to January 2016 were retrospectively studied, and the patients' age, gender, left and right limb condition were recorded. The patients were divided into two groups according to Blumensaat angle measured on the MRI: group A(Blumensaat angle<=0°), and group B(Blumensaat angle >0°). The ROC curve was drawn from the statistical data of the group B to get the best critical value of the anterior cruciate ligament injury when the Blumensaat angle was more than 0°. According to the best critical value obtained by ROC curve, the coincidence rate of the total sample was obtained.

There were no significant differences in patients' age, gender, and affected limbs. There were 51 patients in group A, in which 49 patients were diagnosed as anterior cruciate injury under arthroscopy(gold standard for diagnosis of anterior cruciate ligament injury), and 2 patients were diagnosed as no anterior cruciate injury under arthroscopy. When the Blumensaat angle was<0°, the coincidence rate was 96.07%. In group B(116 cases), the area under the ROC curve was 0.910, the best cutoff corresponds to 15°; the sensitivity was 70.0%, and the specificity was 95.8%. When the Blumensaat angle was >=15°, the probability of anterior cruciate ligament injury was greater. When the Blumensaat angle was 0° to 15°, the anterior cruciate ligament was more likely to be not injured. The Blumensaat angle<=0°or>=15° were used to diagnose the injury of anterior cruciate ligament. Compared with the results of arthroscopy, the coincidence rate of the total sample was 92.8%.

Blumensaat angle is helpful to diagnose the ACL injuries. When the Blumensaat angle was <=0° or >=15°, the probability of ACL injury is greater.