Abstract
Quantifying the effect of routing and topology of the inter-connected finger extensor mechanism on hand grasping performances is a long-standing research problem for the better clinical diagnosis, surgical planning and biomimetic hand development. However, it is technically demanding to measure the hand performance parameters such as the contact forces and contact area during hand manipulation. It is also difficult to replicate human hand performance through the physical hand model due to its sophisticated musculotendinous structure. In this study, an experimental validated subject-specific finite element (FE) human hand model was used for the first time to quantify the influence of different tendon topologies and material properties on hand grasping quality. It is found that the grasping quality is reduced by 15.94% and 8.54% if there are no extensor hood and lateral band respectively, and the former plays a more important role in transmitting forces and maintaining grasping qualities than the latter. Excluding extensor hood in the topology causes more reductions in hand contact pressure and contact area than omitting lateral band. 7.5% of the grasping quality is lost due to a softened tendon with half of its original Young's Modulus. Hardened extensor tendon does increase the grasping quality, but the enhancing effect tends to level off once the tendon Young's Modulus is increased by more than 50%. These results prove that the lateral band and extensor hood are critical components for maintaining grasping quality. The dexterity and grasping quality of robotic and prosthetic hands could be improved by integrating these two components. There is also no need to use very stiff tendon material as it won't help to effectively enhance the grasping quality.
Highlights
During daily human activities, the dexterity of fingers and the grasping performance are maintained by the forearm and intrinsic muscles through the musculotendon network and the constraint forces provided by the joint capsules, ligaments and joint articular surfaces [1, 2]
Modulus is increased by more than 50%. These results prove that the lateral band and extensor hood are critical components for maintaining grasping quality
The finite element (FE) hand model with intact extensor mechanism was validated against the in-vivo grasping experimental data
Summary
The dexterity of fingers and the grasping performance are maintained by the forearm and intrinsic muscles through the musculotendon network and the constraint forces provided by the joint capsules, ligaments and joint articular surfaces [1, 2]. Together with the extensor pollicis longus (EPL) muscle are regarded as the main dorsal forearm muscles for Yuyang Wei is with Department of Mechanical, Aerospace and Civil. Engineering, The University of Manchester, Manchester, UK The inter-connected and retinacular ED tendon spanning over the 2nd to 5th digits is recognized as the extensor mechanism or dorsal aponeurosis. This web-like tendon originates from the controlling muscles of the hand and inserts into the phalanges. The muscles associated with hand kinematics are coordinated by a set of retinacular structures of the extensor mechanism to achieve the high dexterity and grasping quality of human hand [3, 4]. The analysis on biomechanics of extensor mechanism and its contributions to grasping capacities may help to understand the etiology of hand diseases, surgical planning, and the design of robotic and prosthetic hand
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