Femorotibial angle scan–rescan reproducibility: a high‐precision calculation on a large cohort
Author(s)
Hall, Thomas AG
Jones, Gareth G
van Arkel, Richard J
Type
Journal Article
Abstract
Purpose
Femorotibial angle (FTA) is a convenient measure of coronal knee alignment that can be extracted from a short knee radiograph, avoiding the additional radiation exposure and specialist equipment required for full-leg radiographs. While intra- and inter-reader reproducibility from the same image has been reported, the full scan–rescan reproducibility across images, as calculated in this study, has not.
Methods
In this study, 4589 FTA measurement pairs from 2586 subjects acquired a year apart were used to estimate FTA scan–rescan reproducibility using data from the Osteoarthritis Initiative. Subjects with radiographic progression of osteoarthritis or other conditions that may cause a change in coronal knee alignment were excluded. Measurement pairs were analysed using paired-samples mathematical equation tests to detect differences and compared to symptomatic changes in Western Ontario and McMaster Universities Arthritis Index scores for joint pain, stiffness and physical function to detect correlations.
Results
The 95% limit of agreement and the paired-samples correlation were calculated with high precision to be [−1.76°, +1.78°] and 0.938, considerably worse than the corresponding figures for intra- and inter-reader reproducibility, without relation to symptomatic or radiographic changes in knee condition. This error will weakly attenuate mathematical equation and mathematical equation values from their true values in correlative studies involving FTA. The realistic maximum value for mathematical equation is 87% and for Pearson's mathematical equation is 93%.
Conclusion
The scan–rescan reproducibility in FTA is almost double the intra- and inter-reader reliability from a single scan. At almost ±2° accuracy, FTA is inappropriate for surgical use, but it is sufficiently reproducible to produce good correlations in studies predicting disease incidence and progression.
Level of Evidence
Level II, retrospective study.
Femorotibial angle (FTA) is a convenient measure of coronal knee alignment that can be extracted from a short knee radiograph, avoiding the additional radiation exposure and specialist equipment required for full-leg radiographs. While intra- and inter-reader reproducibility from the same image has been reported, the full scan–rescan reproducibility across images, as calculated in this study, has not.
Methods
In this study, 4589 FTA measurement pairs from 2586 subjects acquired a year apart were used to estimate FTA scan–rescan reproducibility using data from the Osteoarthritis Initiative. Subjects with radiographic progression of osteoarthritis or other conditions that may cause a change in coronal knee alignment were excluded. Measurement pairs were analysed using paired-samples mathematical equation tests to detect differences and compared to symptomatic changes in Western Ontario and McMaster Universities Arthritis Index scores for joint pain, stiffness and physical function to detect correlations.
Results
The 95% limit of agreement and the paired-samples correlation were calculated with high precision to be [−1.76°, +1.78°] and 0.938, considerably worse than the corresponding figures for intra- and inter-reader reproducibility, without relation to symptomatic or radiographic changes in knee condition. This error will weakly attenuate mathematical equation and mathematical equation values from their true values in correlative studies involving FTA. The realistic maximum value for mathematical equation is 87% and for Pearson's mathematical equation is 93%.
Conclusion
The scan–rescan reproducibility in FTA is almost double the intra- and inter-reader reliability from a single scan. At almost ±2° accuracy, FTA is inappropriate for surgical use, but it is sufficiently reproducible to produce good correlations in studies predicting disease incidence and progression.
Level of Evidence
Level II, retrospective study.
Date Issued
2024-12
Date Acceptance
2024-06-26
Citation
Knee Surgery, Sports Traumatology, Arthroscopy, 2024, 32 (12), pp.3133-3140
ISSN
0942-2056
Publisher
Wiley
Start Page
3133
End Page
3140
Journal / Book Title
Knee Surgery, Sports Traumatology, Arthroscopy
Volume
32
Issue
12
Copyright Statement
© 2024 The Author(s). Knee Surgery, Sports Traumatology, Arthroscopy published by John Wiley & Sons Ltd on behalf of European Society of Sports Traumatology, Knee Surgery and Arthroscopy.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
License URL
Identifier
http://dx.doi.org/10.1002/ksa.12352
Publication Status
Published
Date Publish Online
2024-07-10