{Reference Type}: Journal Article
{Title}: Femorotibial angle scan-rescan reproducibility: A high-precision calculation on a large cohort.
{Author}: Hall TAG;Jones GG;van Arkel RJ;
{Journal}: Knee Surg Sports Traumatol Arthrosc
{Volume}: 0
{Issue}: 0
{Year}: 2024 Jul 10
{Factor}: 4.114
{DOI}: 10.1002/ksa.12352
{Abstract}: <B>OBJECTIVE: </B>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.<BR><B>METHODS: </B>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   t $t$  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.<BR><B>RESULTS: </B>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   R 2  ${R}^{2}$  and  r $r$  values from their true values in correlative studies involving FTA. The realistic maximum value for   R 2  ${R}^{2}$  is 87% and for Pearson's  r $r$  is 93%.<BR><B>CONCLUSIONS: </B>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.<BR><B>METHODS: </B>Level II, retrospective study.