From kellgren-lawrence to calcium pyrophosphate crystal deposition: a soft-labelling framework for knee osteoarthritis assessmen
Francisco Bérchez-Moreno 
Riccardo Rosati 
Víctor Manuel Vargas-Yun 
Luca Romeo 
Pedro Antonio Gutiérrez 
César Hervás-Martínez arXiv preprint arXiv:2605.28176
Abstract
Background and objective. Conventional Deep Learning (DL) approaches for Knee Osteoarthritis (KOA) grading rely on one-hot labels, which fail to capture both the ordinal uncertainty of Kellgren–Lawrence (KL) and Calcium Pyrophosphate Deposition Disease (CPPD) severity scores and the asymmetric relationship between the two scales observed in clinical practice. Methods. We retrospectively collected 2172 knee X-ray images, including 968 radiographs jointly annotated for KL and CPPD severity. An ordinal DL framework based on soft-labelling was developed for both tasks, replacing one-hot targets with unimodal probability distributions centred on the annotated grade. Four formulations were investigated: binomial, beta, triangular, and exponential. Results. All soft-labelling strategies consistently outperformed the nominal baseline. For CPPD grading, the triangular formulation achieved the highest Quadratic Weighted Kappa (QWK) and the lowest Mean Absolute Error (MAE) (QWK = 0.796<sub>0.018</sub>; MAE = 0.438<sub>0.025</sub>), while the beta formulation yielded the most balanced class-wise performance considering Average MAE (AMAE) and Maximum MAE (MMAE) across classes (AMAE = 0.458<sub>0.032</sub>; MMAE = 0.573<sub>0.084</sub>). For KL grading, the beta-based approach provided the best overall performance, achieving the highest QWK together with the lowest MAE and class-wise errors (QWK = 0.777<sub>0.022</sub>; MAE = 0.529<sub>0.031</sub>; AMAE = 0.523<sub>0.031</sub>; MMAE = 0.775<sub>0.136</sub>). Statistical analysis demonstrated significant improvements over conventional one-hot supervision (p<0.001). Conclusions. Overall, the proposed ordinal soft-labelling framework more effectively captured the uncertainty and asymmetric relationship between KL and CPPD severity scales, supporting more reliable and clinically meaningful knee radiograph assessment.
BibTex Citation
@article{Berchez2026From,
author = {B{\' e}rchez-Moreno, Francisco and Rosati, Riccardo and Fiorentino, Maria Chiara and Vargas-Yun, V{\' i}ctor Manuel and Cipolletta, Edoardo and Filippucci, Emilio and Romeo, Luca and Guti{\' e}rrez, Pedro Antonio and Herv{\' a}s-Mart{\' i}nez, C{\' e}sar},
journal = {arXiv preprint arXiv:2605.28176},
year = {2026},
title = {From kellgren-lawrence to calcium pyrophosphate crystal deposition: a soft-labelling framework for knee osteoarthritis assessmen},
url = {https://arxiv.org/abs/2605.28176},
howpublished = {https://arxiv.org/abs/2605.28176},
}
BibTex Unicode Citation
@article{Berchez2026From,
author = {Bérchez-Moreno, Francisco and Rosati, Riccardo and Fiorentino, Maria Chiara and Vargas-Yun, Víctor Manuel and Cipolletta, Edoardo and Filippucci, Emilio and Romeo, Luca and Gutiérrez, Pedro Antonio and Hervás-Martínez, César},
journal = {arXiv preprint arXiv:2605.28176},
year = {2026},
title = {From kellgren-lawrence to calcium pyrophosphate crystal deposition: a soft-labelling framework for knee osteoarthritis assessmen},
url = {https://arxiv.org/abs/2605.28176},
howpublished = {https://arxiv.org/abs/2605.28176},
}
APA Citation
Bérchez-Moreno, F., Rosati, R., Fiorentino, M. C., Vargas-Yun, V. M., Cipolletta, E., Filippucci, E., Romeo, L., Gutiérrez, P. A., & Hervás-Martínez, C. (2026). From kellgren-lawrence to calcium pyrophosphate crystal deposition: a soft-labelling framework for knee osteoarthritis assessmen. arXiv Preprint arXiv:2605.28176. https://arxiv.org/abs/2605.28176
RIS Citation
TY - JOUR
AU - Bérchez-Moreno, Francisco
AU - Rosati, Riccardo
AU - Fiorentino, Maria Chiara
AU - Vargas-Yun, Víctor Manuel
AU - Cipolletta, Edoardo
AU - Filippucci, Emilio
AU - Romeo, Luca
AU - Gutiérrez, Pedro Antonio
AU - Hervás-Martínez, César
DA - 2026///
PY - 2026
ID - temp_id_834147096954
T2 - arXiv preprint arXiv:2605.28176
TI - From kellgren-lawrence to calcium pyrophosphate crystal deposition: a
soft-labelling framework for knee osteoarthritis assessmen
UR - https://arxiv.org/abs/2605.28176
ER -
CV Citation
F. Bérchez-Moreno, R. Rosati, M.C. Fiorentino, V.M. Vargas-Yun (CA), E. Cipolletta, E. Filippucci, L. Romeo, P.A. Gutiérrez, C. Hervás-Martínez (4/9). "From kellgren-lawrence to calcium pyrophosphate crystal deposition: a soft-labelling framework for knee osteoarthritis assessmen". arXiv preprint arXiv:2605.28176, 2026.