The purpose of this study was to create and assess the reliability of an Animal Magnetic resonance imaging Osteochondral Score (AMOS) to evaluate the healing of experimentally created osteochondral defects in preclinical models.
The AMOS score consists of an objective score and four subjective scores (integration, repair tissue surface, infill signal intensity and signal change outside surgical site). The AMOS score was applied to lesions in forty-six sheep using an ovine medial femoral condyle osteochondral defect model as an exemplar. These defects were subsequently evaluated histologically using the modified O’Driscoll score.
The AMOS scores recorded ranged from 35 to 100. The AMOS score had 92.5% inter-rater reliability and 80% intra-rater reliability for the four subjective components. The mean inter-rater-reliability was 85% (+/- >1%) for integration; for intensity of infill, the mean inter-rater reliability was 95% (+/- 0%); the mean intra-reliability was 92.5% (+/- 2.5%) for repair tissue surface; and the mean inter-rater reliability was 97.5% (+/- 2.5%) for signal change outside the operated site. No correlation was found between the AMOS score and the modified O’Driscoll score.
The AMOS score had high inter-rater reliabilities, suggesting that it would be an effective scoring system. The AMOS score is a user-friendly semi-quantitative method of assessing osteochondral defect from magnetic resonance appearance for following ovine defect changes. The lack of correlation between AMOS and histological scorings reflects their different sensitivities to healing, suggesting that the AMOS score is complementary to histological evaluation.