Page 26 - Delaware Medical Journal - September/October 2020

Accuracy and Reliability of Measurement Tools in
the Assessment of Femoral and Tibial Torsion with
Computed Tomography, EOS, and Gait Lab
Carlos Pargas, MD; Adolfredo Santana, MD; Ahmet Imerci, MD; Freeman Miller, MD
Purpose: During treatment of lower extremity deformities, appropriate assessment is required to develop a management plan. The axial plane is a difficult component of the complete analysis. New imaging methods to find an accurate
solution to triplane measurements have emerged. To choose the appropriate technique, accuracy and reliability must be considered. This investigation compared measurements of femoral and tibial torsion from computed tomography (CT), EOS (ArtVentive Medical Group, Inc., San Marcos, CA), and the gait laboratory.
Methods: A plastic anatomy leg skeleton (Evanston, IL) was used to measure the axial plane and compare the accuracy and reliability among these three methods. Similar position of the skeleton model during each test. Pre- and post- osteotomy studies performed, analyzed, and compared. Osteotomy performed in the proximal third of the femur and
in the distal third of the tibia, producing an axial plane deformity of 40° (internal rotation) and 35° (external rotation), respectively.
Results: Eighteen measurements (three pre-osteotomy and three post-osteotomy for each technique) were performed. Mean femoral measurements were for CT, -16.3° external rotation pre-osteotomy and 23.3° internal rotation post- osteotomy with a correction of 39.7°; for EOS, -8.0° external rotation pre-osteotomy and 24.0° internal rotation post- osteotomy with a correction of 32.0°; and for the gait lab, -15.3° external rotation pre-osteotomy and 42.3° internal rotation post-osteotomy with a correction of 57.7°. Mean tibial measurements were for CT, -26° external rotation pre- osteotomy and -60° external rotation post-osteotomy with a correction of 34.0°; for EOS, 4.7° internal rotation pre- osteotomy and -21.0° external rotation post-osteotomy with a correction of 25.7°; and for the gait lab, 3.3° internal rotation pre-osteotomy and -32.0° external rotation post-osteotomy with a correction of 35.3°.
Conclusion: CT is the most precise method to analyze the axial plane in the femur and a good option for the tibia. Due to motion in the hip, the gait laboratory imprecisely analyzed the axial plane in the femur. However, it was the most accurate for the tibia since the knee was limited to flexion-extension movements and there was no soft-tissue artifact. EOS had acceptable results with analyzing rotational problems; however, severe rotational changes affect the outcome because landmarks are more difficult to identify.
Keywords: femoral torsion, tibial torsion, EOS, gait lab, CT scan
218 Del Med J | September/October 2020 | Vol. 92 | No. 5
Abstract