Andrea Rosskopf MD, Presenter: Nothing to Disclose

Leonhard Ramseier, Abstract Co-Author: Nothing to Disclose

Christian W. A. Pfirrmann MD, MBA, Abstract Co-Author: Advisory Board, Siemens AG Consultant, Medtronic, Inc

Florian M. Buck MD, Abstract Co-Author: Nothing to Disclose

Femoral and tibial torsion measurements on 3D models based on low-dose biplanar radiographs (BPR) have been shown to be comparable to state of the art computer tomography (CT) measurements. However, CT measurements as well as BPR measurements are associated with radiation exposure of the child. The aim of our study was to evaluate reliability and interchangeability of femoral (FT) and tibial torsion (TT) measurements in children using magnetic resonance (MR) imaging compared to measurements on 3D models based on low-dose biplanar radiographs.

Institutional review board waiver was obtained. FT and TT were measured in 30 children (mean age 10.1 years; range 6.2 – 15.6 years; 14 female) using axial MR images of the hip, knee and ankle by two independent readers. They were compared to measurements on BPR of the lower limb based on 3D models by two separate independent readers. Interreader and intermethod agreement was calculated using descriptive statistics, Intraclass correlation coefficient (ICC) and Bland-Altman analysis.

FT/TT was -6° – 47°/+1° – 44° on MR images and -13° – 46°/9°– 49° for measurements on BPR 3D models. The average difference between the two methods was 4.6° ± 4.1/6.0° ± 3.8, respectively. Interreader agreement (ICC) of FT/TT measurements was 0.97/0.96 on MR images and 0.99/0.94 on BPR 3D models. Intermethod agreement (ICC) for MR measurements was 0.93 (95% confidence interval [CI], 0.88 – 0.96) for FT and of 0.87 (CI, 0.39 – 0.95) for TT. Mean measurement differences between the two BPR readers were 2.1° (0.0° – 7.0°) for FT and 3.4° (0.0° – 12.0°) for TT. Mean interreader differences at MR were 3.2° (0.1° – 8.0°) for FT and 3.5° (0.1° – 9.5°) for TT. Bland-Altman plots showed a systematic underestimation of TT on MR measurements compared to BPR 3D models of 5°. All but 3/4 measurements of FT/TT were within the 95% limit of agreement.  

FT and TT measurements in children using MR images are comparable to measurements on BPR 3D models.

Femoral and tibial torsion measurements in children can be reliably performed without radiation exposure based on axial magnetic resonance images.

Rosskopf, A, Ramseier, L, Pfirrmann, C, Buck, F, Femoral and Tibial Torsion Measurements in Children: Comparison of MR Imaging and 3D Models based on Low-dose Biplanar Radiographs  .  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14045647.html