Civil Engineering Reference
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TABLE 45.7 Location of Finger Joint Centers from Distal End of Phalanx. DIP Distances as percen-
tage of Medial Phalanx Length, PIP and MCP Distances as Percentage of Proximal Phalanx Length
Finger
DIP
PIP
MCP
Index
18
13
20
Middle
15
12
20
Ring
13
12
19
Little
17
14
24
Source: Adapted from An, K.N., Chao, E.Y., Cooney, W.P., and Limscheid, R.L. (1979). Journal of
Biomechanics, 12:775-788. With permission.
Landsmeer's (1960) Model III depicts a tendon running through a tendon sheath held securely against
the bone, which allows the tendon to curve smoothly around the joint (Figure 45.8c). The tendon
displacement is described by:
2
u
d
2
u
1
= tan
1
x
¼
2 y
þ
y
(45
:
3)
where y is the tendon length to joint axis measured along the long axis of the bone and d is the distance of
tendon to the long axis of the bone.
For small angles of flexion (u
,
20
8
), tan u is almost equal to u, and Equation (45.3) simplifies to:
x
¼
d u
(45
:
4)
Armstrong and Chaffin (1979) proposed a static model for the wrist based on Landsmeer's (1962)
tendon Model I and LeVeau's (1977) pulley-friction concepts (Figure 45.9). Armstrong and Chaffin
(1978) found that, when the wrist is flexed, the flexor tendons are supported by flexor retinaculum
on the volar side of the carpal tunnel. When the wrist is extended, the flexor tendons are supported
by the carpal bones. Thus, deviation of the wrist from neutral position causes the tendons to be
displaced against and past the adjacent walls of the carpal tunnel. They assumed that a tendon sliding
over a curved surface is analogous to a belt incurring friction forces while wrapped around a pulley.
The radial reaction force on the ligament or the carpal bones, F
R
, can be characterized as follows:
2F
T
e
mQ
sin (u
F
R
¼
=
2)
(45
:
5)
TABLE 45.8 Representative Tendon Insertion Distances for Each Finger with Respect to that Joint Center Coordi-
nate System (Figure 45.7). DIP distances as percentage of Medial Phalanx Length, PIP and MCP Distances as
percentage of Proximal Phalanx Length
Index Finger
Middle Finger
Ring Finger
Little Finger
Distal
Proximal
Distal
Proximal
Distal
Proximal
Distal
Proximal
Joint Muscle
x
y
x
y
x
y
x
y
x
y
x
y
x
y
x
y
DIP
FDP
2
18
2
13
25
2
22
2
19
2
12
26
2
22
2
19
2
13
26
2
22
2
18
2
15
2
2
20
PIP
FDP
2
22
2
14
18
2
17
2
27
2
15
22
2
14
2
28
2
16
23
2
16
2
24
2
15
20
2
18
FDS
2
22
2
11
18
2
13
2
27
2
11
22
2
12
2
28
2
13
23
2
13
2
24
2
13
20
2
15
MCP
FDP
2
24
2
17
13
2
27
2
30
2
18
16
2
26
2
31
2
16
17
2
26
2
27
2
20
15
2
28
FDS
2
24
2
22
13
2
31
2
30
2
18
16
2
31
2
31
2
19
17
2
29
2
27
2
24
15
2
32
Source: Adapted from An, K.W., Chao, E.Y., Cooney, W.P., and Limscheid, R.L. (1979). Journal of Biomechanics, 12:
775-788. With permission.
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