Biomedical Engineering Reference
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sternum; the acromio-clavicular joint, which articulates the scapula by its acro-
mion onto the distal end of the clavicle; the scapulo-thoracic joint, which allows
the scapula to glide on the thorax; and the gleno-humeral joint, which allows the
humeral head to rotate in the glenoid fossa of the scapula.
Another method takes into consideration the final gross movement of the joint
(
Abdel-Malek et al., 2001a
d
), as abduction/adduction (about the anteroposterior
axis of the shoulder joint), flexion/extension and transverse flexion/extension
(about the mediolateral axis of the shoulder joint). Note that these motions pro-
vide for three rotational degrees of freedom having their axis intersecting at one
point. This gives rise to the effect of a spherical joint typically associated with
the shoulder joint (
Figure 2.18
). In addition, the upward/downward rotation of the
scapula gives rise to two substantial translational degrees of freedom in the shoul-
der complex. This sliding motion is represented by elevation/depression, protrac-
tion/retraction,
tipping forward/backward and medial/lateral
rotations for
the
scapulo-thoracic joint (5 DOF).
This model allows for consideration of the coupling between some of the
joints as is the case in the shoulder where muscles extend over more than one seg-
ment. When muscles are used to lift the arm in a rotational motion, unwittingly, a
translational motion of the shoulder occurs.
The hand is composed of many small bones called carpals, metacarpals, and
phalanges. The two bones of the lower arm—the radius and the ulna—meet at the
hand to form the wrist. We will model the wrist as three intersecting revolute
joints intersecting at one point, whose action yields a spherical wrist (
Pieper,
1968
). The complete 9-DOF model of
the upper extremity is
shown in
Figure 2.19
.
q
4
q
2
y
o
q
1
q
3
x
o
q
5
q
q
7
q
9
X(
θ)
q
8
FIGURE 2.19
Modeling of the upper extremity as a 9-DOF kinematic chain.
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