Value of dualenergy CT in diagnosis of occult fracture of knee joint

LI Wen-wen; ZHANG Yi; LIU Kai; LI Bo; DING Juan

doi:10.16048/j.issn.2095-5561.2024.05.11

Abstract：Objective To investigate the diagnostic value of dual energy CT(DECT)virtual decalcification(VNCa)in occult fracture of knee joint.Methods A total of 30 cases with acute knee joint trauma admitted to the 960th Hospital of the PLA Joint Logistics Support Force from February 2024 to May 2024 were selected,and all of them had clear history of trauma and knee mobility disorder.All the patients were examined by knee joint DECT and MRI.Each knee joint was divided into 12 regions(6 regions in the upper tibia and 6 regions in the lower femur),and the bone marrow edema of the knee joint was evaluated on VNCa images,and the detection rate of bone marrow edema in each region was recorded.Using MRI images as the reference standard,the qualitative diagnostic efficacy of DECT for occult fractures was evaluated.CT values of the mixed weighted images with a fusion coefficient of 0.5(similar to 120 kV conventional images,hereinafter referred to as conventional images)and VNca images of the bone marrow edema positive area of the lower femur,the bone marrow edema positive area of the upper tibia and the corresponding normal areas were measured,and the difference of CT values was calculated and compared.Receiver operating characteristic(ROC)curve was drawn to evaluate the diagnostic value of DECT in knee bone marrow edema.Results There were 360 knee areas in 30 patients.MRI showed bone marrow edema in lower femur with 67 areas and upper tibia with 102 areas,and VNCa image showed bone marrow edema in lower femur with 72 areas and in upper tibia with 112 areas.Using MRI as the criterion,the sensitivity,specificity,positive predictive value,negative predictive value and accuracy of DECT VNCa in the diagnosis of bone marrow edema at the lower femur were 92.54%,91.15%,86.11%,95.37%and 91.67%,respectively,which was in good agreement with MRI diagnosis(Kappa value 0.747,P<0.05).Using MRI as the criterion,the sensitivity,specificity,positive predictive value,negative predictive value and accuracy of DECT VNCa in the diagnosis of bone marrow edema at the upper tibia were 94.12%,79.49%,85.71%,91.18%and 87.78%,respectively,which was in good agreement with MRI diagnosis(Kappa value 0.824,P<0.05).The CT value of the lower femur bone marrow edema area in VNCa images was(-19.30±20.31)Hu,which was higher than that of the corresponding normal area at the same level[(-90.30±13.08)Hu],and the difference was statistically significant(P<0.05).The CT value of the upper tibial bone marrow edema area in VNCa image was(-11.25±15.98)Hu,which was higher than that of the corresponding normal area at the same level[(-97.02±14.01)Hu],and the difference was statistically significant(P<0.05).ROC curve showed that the area under ROC curve of VNCa image CT value for diagnosing bone marrow edema of lower femur and upper tibia was 0.819,0.857,with the sensitivity of 85.70%,78.10%,and the specificity of 78.57%,93.33%,respectively.ROC curve showed that the area under ROC curves of conventional image CT difference value for diagnosing bone marrow edema of lower femur and upper tibia was 0.740,0.734,with the sensitivity of 64.30%,76.69%,and the specificity of 92.86%,68.75%,respectively.ROC curve showed that the area under ROC curves of VNCa image CT difference value for diagnosing bone marrow edema of lower femur and upper tibia was 0.804,0.859,with the sensitivity of 71.40%,93.32%,and the specificity of 85.71%,84.38%,respectively.Conclusion DECT VNCa can visually observe the bone marrow edema area of occult fractures,and has a high consistency with MRI in evaluating knee bone marrow edema,providing a basis for clinical diagnosis of occult fractures.CT values measured on VNCa images can be used for quantitative assessment of bone marrow edema.