Civil Engineering Reference
In-Depth Information
TABLE 45.3 General Characteristics of the FDP and FDS Tendons
Resting Fiber
Length (cm)
a
Relative Force of Finger
Flexors (%)
c
Moment Arm (cm)
b
DIP joint
PIP joint
MCP joint
Finger
FDP
FDS
FDP
FDS
FDP
FDS
FDP
FDS
FDP
FDS
FDP
/
FDS
Index
6.6
7.2
0.65
—
0.98
0.83
1.01
1.21
2.7
2.0
1.35
Middle
6.6
7.0
0.70
—
1.07
0.87
1.16
1.40
3.4
3.4
1.00
Ring
6.8
7.3
0.68
—
1.04
0.85
1.04
1.30
3.0
2.0
1.50
Little
6.2
7.0
0.60
—
0.85
0.74
0.89
0.98
2.8
0.90
3.11
a
Brand et al. (1981).
b
Ketchum et al. (1978).
c
Brand and Hollister (1993).
weight is supported by the fingers, such as rock climbing. Although, the A3 pulley is relatively weaker and
closer to the PIP joint, it is more flexible and stretches, transferring the load to the A2 and A4 pulleys,
which then fail first (Marco et al., 1998).
45.1.6 Wrist Mechanics
The seven main muscles involved in wrist and hand motion are flexor carpi radialis (FCR), flexor carpi
ulnaris (FCU), flexor digitorum profundus (FDP), flexor digitorum superficialis (FDS), extensor carpi
radialis brevis (ECRB), extensor carpi radialis longus (ECRL), and extensor carpi radialis ulnaris
(ECU) (Garcia-Elias et al., 1991). FCR, FCU, ECRB, ECRL, and ECU's primary function is to move
the wrist, while FDP and FDS are secondary wrist movers. FDP and FDS's primary function is to flex
and extend the fingers and secondarily to rotate the wrist. The FDP and FDS pass through carpal
tunnel. The primary muscles and tendons involved with wrist movements of flexion, extension, radial
and ulnar deviation planes are listed below (An et al., 1981):
Flexion: FCR and FCU
Extension: ECRB, ECRL, and ECU
Radial deviation: FCR, ECRB, and ECRL
Ulnar deviation: FCU, and ECU
The parameters that have been commonly used to describe the muscles are muscle fiber length (FL)
and physiological cross-sectional area (PCSA). Muscle length is related to mechanical potential for
tendon excursion, and the maximum tension of the muscle to its PCSA (An et al., 1991). In moving
the wrist, each tendon across the wrist joint slides a certain distance to execute the movement, and
the tendon excursion and moment arm at various wrist joint angles can be measured and derived
through experiments (Armstrong and Chaffin, 1978; An et al., 1991). Muscle parameters, tendon excur-
sions, and moment arms at wrist joint (An et al., 1981; Lieber et al., 1990; An et al., 1991) are summarized
in Table 45.4. The magnitudes of tendon excursion were measured over a 100
8
range of motion in the
Y
Medial
Proximal
Distal
X
DIP
PIP
MCP
Z
FIGURE 45.5
FDP and FDS tendons of a typical digit.
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