## 2 Materials and Methods
### Boundary and Contact Conditions  
The final finite-element model has 40 solid bodies with contact and joint. The simulations were performed in the ANSYS Mechanical APDL application package (ANSYS Inc., Canonsburg, PA, USA). Two types of contact and one type of joint are provided in the  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{2}{c}{**Hyperelastic**} & \multicolumn{1}{c}{**Reference**} \\  & \multicolumn{2}{c}{**Parameter**} & \multicolumn{1}{c}{**Reference**} \\ \hline
**Tissues** & \(\alpha\) & \(\mu\) [Pa] & \\ \hline Annular ligaments & 10.9 & 24.900 & Main E.K. et al. [18] \\ Transverse ligament & 10.9 & 24.900 & Main E.K. et al. [18] \\ Flexor digitorum deep tendon & 8.89 & 37.600 & Main E.K. et al. [19] \\ Flexor digit superficial tendon & 8.89 & 37.600 & [PERSON] et al. [19] \\ Subsynovial connective tissue & 4.51 & 12.500 & [PERSON] et al. [22] \\ Median nerve & 6.5 & 12.900 & [PERSON] et al., [PERSON] et al. [19; 20] \\ \hline  & \multicolumn{2}{c}{**Elastic**} & \\ \hline  & \(\
u\) & \(E\) [MPa] & \\ Phalanges and carpal bones & 0.3 & 10,000 & [PERSON] et al. [25] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Mechanical properties of the tissues used in model.  
Figure 1: Geometry of the model (**b**) based on MRI (**a**).  
model according to the physiological and anatomical features of the wrist. The first contact type is \"bonded\". In this contact, defined geometries act like one body. Bodies cannot move (no slide and no separate) and rotate between each other. This way the tendon attachment to the phalanges is simulated. The second contact type is \"no separation\". Once the contact is detected, the target and contact surface are tied up for the rest of the analysis. Slide is possible, but the nodes in contact are bonded to the target surface in a normal direction. This type of contact simulates the interaction of tendons and annular ligaments. The only type of joint is \"Revolute\". A joint typically serves as a junction where bodies are joined together. Joint types are characterized as fixed or free depending on their rotational and translational degrees of freedom.  
A Revolute type means five constrained degrees of freedom with all axis motion and rotation around X and Y axes. Thus, only one free degree of freedom is available, i.e., rotation around Z axis. This simulates the flexion/extension of the fingers and wrist. Details of the contact of all bodies can be found in Table 2.  
The finite-element mesh was generated according to the contact interactions of the bodies. Hexahedral and tetrahedral elements were used. Hexahedral elements predominated in the areas of the tendon, SSCT, transverse ligament, and annular ligaments. Tetrahedral elements predominate in the phalanges of the fingers. The whole model included 422,779 nodes and 122,486 elements.  
Four sets of boundary conditions were chosen to simulate finger flexion, wrist extension, subsequent fingers flexion and wrist flexion. The stress-strain state was determined for all 40 solids bodies by finite-element modeling with static analysis. The proximal SSCT region was rigidly fixed in all three cases. The carpal bones were modeled in this way. The median nerve was rigidly fixed at the proximal and distal areas.