Development and Verification of an Anthropomorphic Mechanical Finger Model in OpenSim

Abstract

Background: Computational musculoskeletal models are valuable for understanding finger biomechanics and aiding in medical applications such as postoperative therapy and surgical planning. These models simulate various scenarios and predict outcomes by representing the biomechanical system through equations of motion. However, the complex mechanics of the human finger, particularly the role of the Lateral Bands in coordinated joint flexion, have primarily been studied in static simulations. Their role in dynamic simulations, especially with the inclusion of other key tendons and ligaments, has not been researched.
Aim: This study aims to develop a musculoskeletal model to enhance our understanding of the contribution of Lateral Bands to coordinated finger flexion, by combining insights from previous research to address existing gaps in finger biomechanics. The model will replicate the anatomical joints and Lateral Band structures of an anthropomorphic mechanical finger, offering a simplified design to reduce simulation complexity and enhance verification reliability.
Method: An adapted anthropomorphic mechanical finger was created based on previous work, scaled down to reduce weight and required actuation force. The simulation model was developed in OpenSim, using bone geometries from CAD files and direct measurement attachment location of tendons and ligaments from the mechanical finger for improved accuracy. Model verification involved comparing the model’s behavior with the mechanical finger through experiments focusing on finger flexion under external deep flexor tendon load, using motion capture data, inverse kinematics (IK), and forward dynamics (FD). Results The simulation model accurately replicated the mechanical finger’s joint kinematics, with an average squared error ranging from 1.54e−3 mm to 9.55e−3 mm and an average marker RMSE of ±0.65 mm. Tendon displacement and moment arm were verified with average errors ±1 mm and ±1.23 mm, respectively, indicating that the model closely matches the mechanical finger’s tendon force and joint torque relationships. The model demonstrated that Lateral Bands are essential for interphalangeal joint (IPJ) coupling, as they adjust their tension by becoming taut or slack during finger flexion to distribute forces effectively. Without these Lateral Bands, finger flexion leads to unrealistic joint movements in mechanical finger models. Additionally, the Lateral Bands play a significant role in generating tension in the deep flexor tendon during IPJ coupling.
Conclusion: This study demonstrated the role of Lateral Bands during dynamic finger flexion by incorporating anatomically-based structures and replicating their behavior. The findings provide deeper insights into their function and set a new foundation for future research. Additional studies could further explore how Lateral Bands influence force distribution and joint mechanics, potentially leading to better understanding and treatment of finger injuries and disorders.