Upper Extremity Analysis of the Wrist - Fundamentals and Assessment Tools for Occupational Ergonomics - page 841

45
Upper Extremity
Analysis of the Wrist

45.1 Anatomy of the Hand and Wrist .............. 45-1
Bones of the Hand and Wrist † Joints of the Hand and
Wrist † Muscles of the Forearm, Hand, and
Wrist † The Flexor Digitorum Profundus and Flexor
Digitorum Superficialis † Flexor Tendon Sheath Pulley
Systems † Wrist Mechanics † Select Anthropometry Data
45.2 Models of the Hand and Wrist . . .............. 45-9
Static Tendon Pulley Models † Dynamic Tendon-Pulley
Models † Complex Tendon Models † A Two-Dimensional
Hand and Wrist Model
45.3 Direct Measurement Studies .................. 45-20
45.4 Data-Driven WRMSD Risk Index .............. 45-21
45.5 Conclusions

Andris Freivalds
Pennsylvania State University

. ............................. 45-25

45.1 Anatomy of the Hand and Wrist

45.1.1 Bones of the Hand and Wrist
The human hand has 27 bones divided into three groups: 8 carpal bones in the wrist, 5 metacarpal bones,
and 14 phalanges of the fingers. The carpal bones are arranged in two rows and have names reflecting
their shapes (Figure 45.1). The bones of the distal row, from the lateral side to the medial side,
include the trapezium (four sided with two parallel sides), the trapezoid (four sided), the capitate
(the central bone), and the hamate (hook shaped). These four bones fit together, tightly bound by inter-
osseous ligaments to form a relatively immobile unit that articulates with the metacarpals to form the
carpometacarpal (CMC) joint. The bones of the proximal row include the scaphoid (boat shaped),
the lunate (half-moon shaped), the triquetrum (triangle shaped), and the pisiform (pea shaped). The
proximal surfaces of the scaphoid, lunate, and triquetrum form a biconvex elliptical surface which articu-
lates with the biconcave surface of the distal extremity of the radius. The articulation between the prox-
imal and distal rows is term the midcarpal joint while articulations between adjacent bones are called
intercarpal joints.
The five metacarpal bones are cylindrical in shape and articulate proximally with the distal carpal
bones and distally with the proximal phalanges of the digits. The base of the metacarpal bones of the
index and middle fingers are linked together tightly and articulate little with the trapezoid and the capi-
tate bones in the CMC joint. On the other hand, the CMC joint for metacarpals of the ring and little
fingers with the hamate allow up to 10 extension, respectively. The

arched shafts of the metacarpal bones form the palm and the distal ends are spherical in shape, allowing

8 -15 8 and 20 8 -30 8 of flexion

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45-1