Civil Engineering Reference
In-Depth Information
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FIGURE 45.6 Pulley structure of the finger. (Adapted from Nordin, M. and Frankel, V.H. (2001). Basic Mechanics of
the Musculoskeletal System, 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins. With permission.)
flexion-extension plane and a 50
8
range of motion in the radial -ulnar deviation plane in forearm
neutral position.
Table 45.4 reveals that the FCR, FCU, and ECRB provide larger tendon excursion during flexion and
extension movement than ECRL and ECU, while ECRL and ECU have greater tendon excursion during
radial and ulnar deviation movement. The results also demonstrate that the FCR and FCU are prime
muscles for flexion, ECRB for extension, ECRL for radial deviation, and ECU for ulnar deviation. In
spite of the three-dimensional orientation of the wrist tendons to the rotation axes and the complexity
of carpal bone motion, Table 45.4 indicates that the moment arms of wrist motion are maintained fairly
consistently and correspond well with the anatomical location of the tendons. According to An et al.
(1991), these findings are related to the anatomical considerations; the extensor retinaculum ensures a
consistent relationship of the wrist extensors (ECRB, ECBL, and ECU) to the rotation axes, while the
FCR is firmly fixed in the fibro-osseous groove, and the FCU infixed on the pisiform.
45.1.7 Select Anthropometry Data
For any sort of biomechanical modeling it is necessary to have a variety of key anthropometric properties,
such as segment link lengths, segment weights, the location of the center of gravity, the location of the
center of joint rotation, the range of motion for each joint, and muscle insertion points. Not all of this
information has been measured or documented at the level of individual phalanges, but the following
tables may provide some useful data: Table 45.5 — phalange lengths, Table 45.6 — interphalangeal
joint dimensions, Table 45.7 — joint center locations, and Table 45.8 — tendon insertion points.
The latter two tables were adapted from the data of An et al. (1979) based on three separate coordinate
systems located at the center of joint rotation for each phalanx as shown in Figure 45.7. Note the x-axis is
in the axial direction of the phalanx, with the positive direction pointing proximally. The y-axis is per-
pendicular with the positive direction pointing dorsally. The positive z-axis points radially for the right
hand. However, any deviations in the z-direction were generally minimal and were omitted for simplicity.
The tendon insertion points of Table 45.8 correspond approximately to the location of the five annular
pulleys. This still allows for adequate modeling of finger flexion in the x-y plane. Other, more functional,
TABLE 45.4 Physiological and Mechanical Properties of Wrist Joint Muscles and Tendons
Moment Arm (mm)
a
Physiological Size
Tendon Excursion (mm)
PCSA (cm
2
)
Muscle and Tendon
Length (cm)
F
/
E plane
R
/
U plane
F
/
E plane
R
/
U plane
FCR
10.9-12.4
2.0
25 +4
7 +1
þ15 +3
þ8+ 2
FCU
15.2-15.4
3.2-3.4
28
+
4
12
+
3
þ
16
+
3
2
14
+
3
ECRB
13.8-15.8
2.7-2.9
20
+
3
11
+
1
2
12
+
2
þ
13
+
2
ECRL
11.8-18.3
1.5-2.4
12
+
3
17
+
1
2
7
+
2
þ
19
+
2
ECU
13.6-14.9
2.6-3.4
10
+
2
16
+
2
2
6
+
1
2
17
+
3
a
denotes extension and ulnar deviation.
Sources: Adapted from, An, K.N., Hui, F.C., Morrey, B.F., Linscheid, R.L., and Chao, E.Y.S. (1981). Journal of Biomechanics,
14:659-669; Lieber, R.L., Fazeli, B.M. and Botte, M.J. (1990). Journal of Hand Surgery, 15:244-250; An, K.N., Horii, E., and
Ryu, J. (1991). Biomechanics of the Wrist Joint, New York: Springer Verlag, pp. 157-169. With permission.
þ
Denotes flexion and radial deviation, and
2
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