## 6 Discussion  
In this study, we assumed that the fluid flow is ruled by a modified version of [PERSON]'s law (Equation (1)). According to Equation (1), the fluid flow is not steady as modelled by the classical [PERSON]'s law. Instead the fluid flow rate evolves with time, more specifically  
Figure 5: Graphical explanation of the region (central body) /direction (vertical, radial and circumferential) corresponding to the parameters highlighted in Table 5. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & \(\beta\) & \(\lambda_{\beta}\Big{(}\frac{m^{4}}{N\times s^{1-\beta}}\Big{)}\) & **Medial/Lateral** \\ \hline TK11 BV & 0.0242 & \(4.744\times 10^{-10}\) & M \\ \hline TK11 BR & 0.0512 & \(5.04\times 10^{-10}\) & M \\ \hline TK11 BC & 0.0220 & \(5.018\times 10^{-10}\) & M \\ \hline TK16 PR & 0.0426 & \(4.619\times 10^{-10}\) & L \\ \hline TK16 AR & 0.0259 & \(1.695\times 10^{-10}\) & L \\ \hline TK16 AV & 0.0178 & \(0.765\times 10^{-10}\) & L \\ \hline TK16 PV & 0.0227 & \(0.1083\times 10^{-10}\) & L \\ \hline TK16 BV & 0.0397 & \(4.292\times 10^{-10}\) & L \\ \hline TK16 BC & 0.0655 & \(10.926\times 10^{-10}\) & L \\ \hline TK16 BR & 0.0666 & \(10.822\times 10^{-10}\) & L \\ \hline TK17 AR & 0.0259 & \(1.331\times 10^{-10}\) & L \\ \hline TK17 BV & 0.0553 & \(2.695\times 10^{-10}\) & L \\ \hline TK17 BC & 0.0434 & \(4.318\times 10^{-10}\) & L \\ \hline TK18 BV & 0.0322 & \(1.377\times 10^{-10}\) & M \\ \hline TK18 BR & 0.0287 & \(1.897\times 10^{-10}\) & M \\ \hline TK18 BC & 0.0289 & \(3.823\times 10^{-10}\) & M \\ \hline TK36 BC & 0.0519 & \(7.877\times 10^{-10}\) & M \\ \hline TK37 BV & 0.0450 & \(7.868\times 10^{-10}\) & L \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The results of the fittings. The first column shows the name of the sample, the second column \(\beta\) shows the order of derivative, the third column \(\lambda_{\beta}\) is the anomalous permeability, and the fourth column specifies if the sample is extracted from a medial (M) or lateral (L) meniscus. it evolves with a fractional time derivative (of order \(\beta\)). Equation (1) also implies that the permeability is anomalous in the sense that its units are a function of the order of the derivative \(\lambda_{\beta}=[\frac{L^{4}}{F^{1-\beta}}]\). The classical Darcy's law was recovered for \(\beta=0\) in Equation (1). In order to estimate how closely both models (classical and fractional Darcy's law) fit the experimental data we compared the RMSE values. We observed in 12/18 fitted experimental tests reported in Table 3 that the RMSE given by the fractional model was lower by 10% with respect to the classical model. Although this might seem insufficient to justify a new theory, it is important to note that this is the first attempt to use this type of model for interpreting the rate of fluid flow inside a biological tissue. We are confident that a more precise experimental set up will give more emphasis of the benefit of having a generalized fractional model that allows for incorporation of the classical one by simply setting \(\beta=0\). Furthermore, it would be interesting to study the evolution of fluid flow inside the meniscus and how it varies both spatially (within the posterior/central/anterior portions) of the tissue and directionally (in the vertical/radial/circumferential directions) considering the parameters in Table 3. A first analysis of the parameters highlights that the values of the order of the fractional derivative \(\beta\) and the anomalous permeability \(\lambda_{\beta}\) are higher for the central body of the meniscus with respect of the anterior and posterior horns.