Overview
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Although there are around 30 individual bones in a complete human arm for the sake of a prosthesis I will focus on the 19 bones that make up the phalanges and metacarpals. The function of the wrist can be replicated without the recreation of each carpal joint. and structures that make up the intricacies of the carpus (wrist).
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Replicating the complete skeletal anatomy of a human arm when creating a prosthesis is not necessary in order to provide identical degrees of freedom in a human arm!
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Mechanical Design of One Finger
Bones of the Hand:
The human hand has 27 degrees of freedom:
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5 in the thumb
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Has an additional degree of freedom compared to the other digital and is represented by its increased freedom of rotational movement
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6 in the wrist
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The wrist has maximum available degrees of freedom ​
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4 in each finger (excluding the thumb)
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3 for extension and flexion (each joint)
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1 for abduction and adduction​​​​​​​
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Carpals:
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Eight short bones form the wrist. The most important of which is the trapezium.​ The trapezium is a short bone that directly connects to the phalanges of the thumb which function as a joint.
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Each individual bone is not necessary when constructing a prosthetic only the structure and function of the trapezium and the wrist movements should be replicated
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Metacarpals:
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These five bones function as the palm of the hand.
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In the construction of a prosthesis, it will be imperative to include some sort of replica for structural support and to provide a path for which an artificial tendon can travel along.​​
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Phalanges (14):
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Phalanges or Phalanx refers to the long bones that make up the digitals​
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There are twelve of these bones three for each finger
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Unlike the other fingers, the thumb only has two phalanges
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It is not only necessary to replicate each phalange to provide similar movement, and degrees of freedom but also to be aesthetically pleasing to the individual.
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Photo: Skeletal Anatomy of Forearm
