## 4 Discussion
The role of MRI in assessing cartilage repair tissue has been widely reported [38], and the imaging results of this study confirmed the literature findings in both treatment groups, with high MOCART 2.0 scores. However, several suboptimal imaging findings were also documented, both in terms of surface integrity and subchondral bone alterations, although these findings did not correlate with clinical results. To this regard, previous studies were controversial in regard the clinical significance of MRI findings. [PERSON] et al. [39] showed that mosaicplasty implants with a better imaging appearance also presented better objective and subjective scores, and [PERSON] et al. [40] confirmed this correlation in patients treated with MACT. Conversely, [PERSON] et al. [41], while demonstrating a good-quality repair tissue at 10 years after MACT, found no correlation between clinical outcome and MRI results. These controversial findings have to be interpreted in light of a meta-analysis investigating the correlation between MRI and clinical outcomes after cartilage repair [42]. In fact, only 28% of the included studies found such correlation, leaving unanswered the question of whether MRI is reliable in predicting clinical outcomes after cartilage repair. Therefore, caution should be recommended when interpreting MRI findings and greater importance should be placed on the patient clinical evaluation. This is especially true in a comparative study such as the current one, aiming at determining the most suitable treatment in patients affected by cartilage lesions. The present study compared both clinical and imaging outcomes of mosaicplasty and MACT at long-term follow-up. The results of these techniques in the literature, evaluated singularly, were confirmed, with good and long-lasting results and a low surgical failure rate. Mosaicplasty and MACT also showed similar overall clinical outcomes and comparable tissue repair quality at MRI evaluation. However, this comparative analysis underlined some interesting aspects. MACT presented better clinical results in relatively larger cartilage lesions, better objective findings, and a lower failure rate compared to mosaicplasty. These findings are inconsistent with the only available comparative analysis of these two techniques at short-term follow-up [19]. In detail, [PERSON] et al. reported a significantly greater symptom improvement 2 years after treatment for mosaicplasty compared to MACT in defects larger than 3.5 cm\({}^{2}\), while no significant difference was found for smaller lesions [19]. On the other hand, in contrast to these results, [PERSON] et al. [43] reported a higher rate of failure in patients with large cartilage lesions treated with mosaicplasty compared to first-generation ACI at long-term follow-up, thus underlining that mosaicplasty is not a suitable option for the treatment of large lesions. This result was confirmed by other authors that investigated the significance of the lesion size for mosaicplasty technique, showing better clinical improvement in patients affected by small lesions [44; 45]. An important aspect related to the lesion size is the number of plugs used to cover the defect being correlated with the clinical outcomes and the failure rate [45]. A limited number of plugs could correlate with better results probably because of the cylindrical shape of the grafts that does not allow optimal coverage of the lesion site by multiple grafts, leaving residual small uncovered areas that might impair or diminish the healing process [46; 47]. Another important aspect that needs to be taken into account when evaluating cartilage procedures is the clinical profiling, aimed at determining the patient and lesion characteristics which may play a prognostic role on the final outcome [48]. Many studies evaluated several factors that can influence the failure rate of both these techniques.