## 4 Discussion  
The main result of our study is that neither the porcine model nor the human model with cadaveric tissue from donors of advanced age (over 75 years old) can provide accurate representations of all the mechanical properties of adult human specimens under 75 years old. However, while neither of the two models offers a clear advantage for a general use in biomechanical in vitro tests, each could be adequate for examining specific characteristics of the sutured meniscal horn. Regarding the resistance to suture-induced traction at the specimen level, no difference was observed between the older and younger human meniscus groups, which partially contradicts our first hypothesis that meniscal tissue from older donors (\(\geq\)75 years) does not adequately represent that of the younger menisci. On the other hand, the porcine model was significantly more resistant than the younger human model at the specimen level, with differences of 172.1% in \(F_{c}\) and 174.1% in \(F_{u}\), as opposed to our second hypothesis. Upon examining resistance at the tissue level in terms of tissue cut-out stress at the meniscus-suture interface, \(S_{c}\), both models exhibited significant differences from the younger human group. Specifically, porcine specimens exhibited tissue with a 57.2%-greater resistance to suture-induced tearing, whereas specimens from donors over 75 years old showed less-resistant tissue, with a 28.7% reduction compared to the human meniscus from younger donors. Regarding deformation, the findings from the comparison between the models opposed those observed in specimen resistance. In particular, the equivalent stiffness modulus, \(m\), of the porcine model did not differ from that of the younger human models, while the human \(\geq\)75 years model showed a 48.1% increase in this elastic parameter compared to the human meniscus \(<\)75 years. Consequently, the adequacy of these two models depends on the interest of the study, a result that partially contradicts both of our initial hypotheses that the meniscal tissue from older donors (\(\geq\)75 years) does not adequately represent that of the younger menisci and that the porcine meniscus is a good surrogate for the human meniscus at an age routinely eligible for repairing. In research on mechanical properties at the specimen level, to analyze the resistance of sutured meniscal roots, the older human meniscus model resulted to be a preferable surrogate model to the porcine model; conversely, if the focus is on issues related to deformation before cut-out initiation in the sutured root zone, the porcine model offers a more accurate representation. For studies at the tissue level, as experimental tests to determine material properties around the sutured root area, neither model resulted to be a reliable surrogate in terms of resistance; but in tests where only tissue deformation prior to cut-out initiation is of interest, opting for the porcine model may be preferable. However, caution is advised in the latter case, as the tissue stresses would be inadequately characterized. The differences found in the suitability of the surrogate models when used in studies evaluating meniscal root resistance at the specimen level or tissue level may be partially attributed to differences in thicknesses observed among the groups. The porcine model offers a surrogate for the human meniscus \(<\)75 years, which has a more resistant tissue, with a 57.2% higher \(S_{c}\). This difference is further accentuated at the specimen level due to the thicker root of the porcine meniscus, resulting in a 172.1%-higher \(F_{c}\) and a 174.1%-higher \(F_{u}\). Conversely, when employing an older human meniscus model as a surrogate, although the tissue is less resistant, with a 28.7%-lower \(S_{c}\), this effect is offset at the specimen level. Likely, the reason is that the meniscal root of the older group was thicker than that of the younger group, resulting in the vanishing of differences at the specimen level.