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Section 1: General Topics
Figure 14
adductors: 1 = pectoralis major, 2 = anterior deltoid, 3 = coracobrachialis. B, Posterior adductors:
1 = latissimus dorsi, 2 = teres major, 3 = posterior deltoid, 4 = long head of the triceps.
the upper limb is brought down by the
posterior segment of the deltoid, long
head of the triceps, latissimus dorsi,
and pectoralis major (Figure 23). Beyond neutral, the motion continues as
extension. Motor units responsible for
extension include the posterior deltoid,
middle deltoid, and subscapularis. As
the degree of extension increases, the
supraspinatus becomes more active.
Throughout extension, the subscapularis and supraspinatus act as prime
stabilizers of the humeral head, with a
range of extension of 60°
When the upper limb is elevated to 90°
in the coronal plane, the distal point
of the limb scans the horizontal plane
and traces an arc of 185° 5 (Figure 25).
The flexors and extensors of the glenohumeral joint control the motion.
Schematic drawings showing adductors at the scapulohumeral joint. A, Anterior
is flexed at 90°, the distal point traces
an arc of internal rotation of 70° and an
arc of external rotation of 100°. With
the shoulder elevated 90° in the coronal
plane, this rotatory capability changes
to 90° of external rotation and 70° of
internal rotation
4,5
(Figure 26).
The infraspinatus is responsible
primarily for external rotation of the
humerus (Figure 12), with varying degrees of assistance provided by the teres
minor and posterior deltoid depending
on the position of the arm. As the arm is
4,5
(Figure 24).
abducted, the posterior deltoid becomes
more important, accounting for 60% of
the strength in 90° of abduction.
6
Internal rotation of the humerus is
produced by the combined action of the
pectoralis major, latissimus dorsi, teres
major, and subscapularis (Figure 12).
As abduction of the arm increases from
Rotatory Capability of the
Shoulder Complex
When the upper limb is held in neutral
rotation at the shoulder and the elbow
0° to 90°, activity of the subscapularis,
pectoralis major, and latissimus dorsi
tends to decrease, whereas activity of
the deltoid increases.
6
Figure 15
abductors or protractors of the scapula. 1 =
serratus anterior, 2 = pectoralis minor.
Schematic drawing showing
Elbow
The elbow joint determines an arc of
motion, E2, with a range from 0° to 150°.
The orientation of the plane of action
is closely influenced by the rotational
position of the shoulder joint. For example, when the arm is elevated in the
coronal plane, the envelope of action E
of the elbow is located in this plane if
the shoulder is in external or internal
rotation.
Although the motion of the elbow
has been classified as a hinge joint, its
motion is better described as a loose
hinge. The instant center of rotation varies throughout the arc of flexion-extension. Because this variation occurs over
a small area, it is considered a single axis
of rotation, passing through the center
of the arcs formed by the trochlear sulcus and the capitellum. Using external
landmarks, this corresponds to a line
passing through the inferior aspect of
the medial epicondyle and the center of
the lateral epicondyle.
The main flexors of the elbow are the
brachialis, biceps, and brachioradialis.
Intricate interactions and a wide range
of participation are accomplished by the
elbow flexors depending on the position
of the forearm, degree of elbow flexion,
and the applied load.
the “workhorse” flexor and is active at
7
8,9
The brachialis is
2
Atlas of Amputations and Limb Deciencies, Fourth Edition © 2016 American Academy of Orthopaedic Surgeons
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Chapter 8: Kinesiology of the Upper Limb
Figure 16
adductors or retractors of the scapula. 1 =
middle trapezius, 2 = rhomboideus minor, 3 =
rhomboideus major, 4 = latissimus dorsi.
Schematic drawing showing
any rotational position of the forearm,
any degree of elbow flexion, and with
or without load applied to the flexing
forearm (Figure 27). Because of the
insertion of the brachialis on the ulna,
there is no influence on activity with
forearm rotation. The biceps is also active throughout a full range of elbow
flexion; however, its activity decreases
during forearm pronation. The greatest
biceps activity occurs with the forearm
in a neutral position and whenever any
resistance is encountered. The brachioradialis is active throughout elbow flexion and, like the brachialis, its activity
is essentially independent of forearm
rotation.
The main extensors of the elbow
include the triceps and the anconeus.
Their activity is not influenced by forearm rotation because of the insertion site
on the ulna. However, activity is heightened with increasing elbow flexion as
well as with an increased load. Contrary
Figure 17
scapula. A, Anterior view. 1 = lower segment of the pectoralis major, 2 = pectoralis minor. B, Posterior view. 1 = levator sc apulae, 2 = rhomboideus m inor, 3 = rhomboid eus major, 4 = latissimus dorsi.
Figure 18
segment of th e pectoralis major, 2 = pec toralis minor, 3 = subclavius. B, Posterio r view. 1 = latissimus
dorsi, 2 = lower segment of the trapezius.
Schematic draw ings showing muscles that contri bute to downward rotation of the
Schematic draw ings showing depressor s of the scapula. A, Anterior view. 1 = lower
© 2016 American Academy of Orthopaedic Surgeons Atlas of Amputations and Limb Deciencies, Fourth Edition
103
Section 1: General Topics
Figure 19
elevators of the scapula. 1 = levator scapulae,
2 = upper segment of the trapezius, 3 = rhomboideus minor, 4 = rhomboideus major.
Schematic drawing showing
Figure 20
elevation in the sagittal plane. Exploration of
space from position 1 to 3 is possible in the
neutral rotational position of the shoulder. Elbow action E2 is present in the pl ane. In position
3, the posterior segment of space is reached
through elbow action.
Schematic drawing showing
Figure 21
motion in the sagittal plane. A posterior arc of
motion from position 3 to 4 is possible through
internal rotation. From position 4 to 1, the limb
derotates to reach the neutral position.
Schematic drawing showing
Figure 22
exors at the sc apulohumeral joint. 1 = anterior
segment of the deltoid, 2 = clavicular segment
of the pec toralis major, 3 = coracobrachialis, 4 =
biceps. The arrow indicates exion.
Atlas of Amputations and Limb Deciencies, Fourth Edition © 2016 American Academy of Orthopaedic Surgeons
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Schematic drawing showing
Figure 23
the extensors at the scapulohumeral joint involved in muscle activity during shoulder extension (arrow) from 90° of shoulder exion.
1 = posterior deltoid, 2 = latissimus dorsi, 3 =
pectoralis major, 4 = teres major, 5 = long head
of the triceps.
Schematic drawing showing
Figure 24
exion at the scapulohumeral joint is 180°, and
no combined rotation is necessary. Extension
is 60°.
Schematic drawing showing
Chapter 8: Kinesiology of the Upper Limb
Figure 25
strate that, in the horizontal plane, the arm can
achieve 140° of exion and 45° of extension.
Schematic drawings demon-
to previous studies,10 the different heads
of the triceps generally are active in a
similar manner throughout motion.
Forearm
Forearm rotation occurs about the proximal and distal radioulnar joints, with
the radius rotating around the ulna.
Rotation of the ulna with respect to the
humerus is also coupled with forearm
rotation. External rotation of the ulna
occurs with supination, and internal
rotation occurs with pronation. When
measured at the wrist, forearm rotation
averages approximately 75° of pronation
to 85° of supination.5 Approximately 17°
of additional pronation and supination
is seen when measured at the hand because of contributions from the radiocarpal and midcarpal joints.
The axis of pronation-supination
is variable in location and dependent
on the distal point of fixation11 (Figure
28). Proximally, the axis passes through
the capitellum and the concave center
of the radial head. Distally, it passes
somewhere between the radial and ulnar
styloid. When the ulna is fixed in position, such as when the forearm and hand
are resting on their ulnar border, the
Figure 26
neutral elevation, external rotation of 100° and internal rotation of 70° is possible. B, With the arm
elevated 90°, external rotation of 90° and internal rotation of 70° is possible.
Figure 27
in supination without resistance; (2) Flexion in neutral without resistance; (3) Flexion in pronation
without resistance; (4) Flexion in supination with resistance. The brachialis is the baseline exor.
The biceps is the reserve exor. Its action is decreased in pronation but increased when the forearm is supine, especially when resistance is encountered. Its action is decreased in pronation. The
brachioradialis is more active against resistance. +++ = maximum activity, ++ = mild activity, + =
minimal activity.
longitudinal axis of pronation-supination passes through the concave center
of the radial head proximally and near
the fovea of the distal ulna distally.12
This axis is oblique to the longitudinal
axis of both the radius and the ulna and
is independent of elbow flexion-extension. The hand makes a circumferential
transposition with the radial styloids
Schematic drawings show rotation at the scapulohumeral joint. A, With the arm in
Schematic drawing demonstrates muscle activity during elb ow exion. (1) Flexion
tracing a large arc of motion. However,
in the average habitual motion, the axis
of rotation passes through the distal end
of the radius and not the ulnar head.13
During this rotatory motion, the distal radius and the ulnar head trace arcs
of motion that are comparable in size.
Starting from the position of supination,
the head of the ulna is extended and
© 2016 American Academy of Orthopaedic Surgeons Atlas of Amputations and Limb Deciencies, Fourth Edition
105
Section 1: General Topics
Figure 28
rotation at the distal radioulnar joint. In habitual
rotation, the axis passes through the middle of
the distal end of the radius (+). From supination
to pronation, the radial styloid traces curve 1
and the head of th e ulna traces curve 2. From su pination (S) to neutra l (N), the head of the ulna is
extended and laterally displaced. From neutral
(N) to pronation (P), it is exed and further laterally displaced. When the axis of motion passes
through the center of the ulnar head, the latter
stays still during rotation, whereas the radial
styloid traces a very large curve (3). The location of the axis of rotation is determined by a
peripheral point of xation.
Schematic drawing showing
laterally translated in the neutral position. In pronation, the ulnar head is
flexed and further displaced laterally.
It is important to note that motion at
the distal radioulnar joint is not purely
rotational. Because of the differing radii
of curvature between the sigmoid notch
of the distal radius and the ulnar head
as well as some inherent ligamentous
laxity, translation in the dorsal-volar direction occurs with forearm rotation. In
addition, in the pronated position, the
obliquity of the radius makes it relatively
shorter than the ulna, producing a more
positive ulnar variance.
The interosseous membrane that
unites the radius and ulna relaxes or
tenses during pronation-supination.
The interosseous distance measured in
the distal, middle, and proximal thirds
of the forearm is largest in the neutral
position and smallest in full pronation14
(Figure 29). Therefore, the tension in
the membrane is minimal in full pronation. During a fall on the outstretched
Figure 29
neutral, and supination. The distance is maximal in neutral and minimal in pronation. (Adapted
with permission from Christensen JB, Adams JP, Cho KO, et al: A study of the interosseous distance
between the radius and ulna during rotation of the forearm. Anat Rec 1968;160:261-271.)
pronated hand, the interosseous membrane is not the main element of pressure transmission to the elbow through
the ulna. When load is applied to the
Schematic drawing showing radiohumeral interosseous distance in pronation,
supination is required or resistance is
encountered (Figure 33). The extensor
carpi radialis longus and brevis may be
accessory supinators.
forearm from a distoproximal direction,
the radius transmits 57% of the load directly to the humerus and 43% to the
15
ulna.
The forearm is pronated primarily by
the pronator quadratus and the pronator
teres (Figure 30). The main pronator is
the pronator quadratus; the action of
the muscle is independent of the position of the elbow. The pronator teres is
a reserve pronator that reinforces power when speed is required or resistance
is applied to the motion16 (Figure 31).
The relative contributions of the accessory pronators, the flexor carpi radia
lis and palmaris longus, to pronation
is debatable. The forearm is supinated
primarily by the supinator muscle (Fig-
ure 32). The biceps is the reserve supinator and reinforces the action when fast
Wrist
The wrist, which acts as a universal
joint, has principal planes of motion
in the sagittal plane (flexion/extension)
and in the coronal plane (radial-ulnar
deviation). It also contributes minimally
to pronation-supination in the transverse plane. In isolated flexion-extension, the wrist develops a spheroid type
of motion envelope E3 (Figure 34) that
permits the hand to move without digital motion.12 However, most activities
require a combination of wrist motions.
-
The combination of wrist extension and
pronation-supination permits the hand
to explore the outer half of a circle. The
flexed wrist, when rotated, permits the
hand to explore the inner half of a circle. This latter motion allows functional
Atlas of Amputations and Limb Deciencies, Fourth Edition © 2016 American Academy of Orthopaedic Surgeons
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Chapter 8: Kinesiology of the Upper Limb
Figure 30
pronators of the forearm. (1) pronator quadratus, main pronator; (2) pronator teres, reserve
pronator; (3) exor carpi radialis, an accessory
pronator; (4) palmaris longus, an accessory pronator.
Schematic drawing showing
activities related to the body. Functionally, the hand is used more frequently
with the wrist extended and radially deviated or with flexion combined with
ulnar deviation.
The carpus consists of the distal carpal row, which includes the trapezium,
trapezoid, capitate, and hamate, and the
proximal carpal row, which is made up
of the scaphoid, lunate, and triquetrum.
The pisiform is not functionally part of
the proximal carpal row because it lies
within the flexor carpi ulnaris and acts
as a sesamoid bone through its articulation with the triquetrum. Although
there is some angular intercarpal rotation between the bones within a row,
the bones of each row move synergistically and can be considered a functional
unit with most wrist motion occurring
at the radiocarpal and midcarpal joints.
In both flexion-extension and radialulnar deviation, the center of rotation
is in the head of the capitate.
Overall, the average range of wrist
flexion and extension is 75° to 90°.
Through the flexion-extension arc,
Figure 31
elbow exed w ithout resistance; (2) pronation w ith the elbow extende d without resistance; (3) pronation against resistance. The pronator quadratus is the main pronator active at all positions of the
elbow. The pronator teres increases in activity only against resistance or when speed is required.
+++ = maximum activity, ++ = mild activity, + = minimal activity.
Schematic drawing demonstrates pronation of the forearm. (1) Pronation with the
the proximal and distal rows move in
similar directions. Wrist flexion, which
produces flexion and ulnar deviation
of both rows, and extension, which
produces extension and radial deviation, generates an overall coupled wrist
motion of flexion-ulnar deviation and
extension-radial deviation. Flexionextension is motored by the pull of the
extrinsic flexor and extensor muscles
on the metacarpal bases. The distal carpal row is pulled in a similar direction
because of the secure association of the
metacarpal bases to the distal carpal at
the second through fifth carpometacarpal joints. The proximal carpal row
follows because of articular contact
and ligamentous attachments to the
distal row. Overall, the midcarpal joint
contributes 60% of the arc of flexion
and the radiocarpal joint contributes
40%. In extension, the midcarpal contributes 34%, with the remaining 66%
Figure 32
ing supinators of the forearm. (1) Supinator,
main supinator; (2) biceps, reserve supinator;
(3) extensor carpi radialis longus and brevis,
questionable accessory supinators. The arrow
indicates supination.
Schematic drawing show-
contributed by the radiocarpal joint17
(Figure 35).
The wrist flexors are the flexor carpi
radialis and ulnaris and the pal maris
longus. The long digital flexors are accessory flexors at the wrist. The wrist
extensors are the extensor carpi radialis
longus and brevis and the extensor carpi
ulnaris. The digital extensors are the
accessory extensors of the wrist.
Lateral motion at the wrist averages 15° to 25° of radial deviation and
25° to 40° of ulnar deviation. With
radial-ulnar deviation, the two carpal
rows demonstrate reciprocating motion
with the proximal carpal row sliding in
the direction opposite of hand movement. During radial deviation, motion
occurs primarily at the midcarpal joint,
with the distal row extending, deviating radially, and translating from a
dorsal to palmar direction. The proximal row flexes and displaces to a less
© 2016 American Academy of Orthopaedic Surgeons Atlas of Amputations and Limb Deciencies, Fourth Edition
107
Section 1: General Topics
pronounced degree in an ulnar direction. During ulnar deviation, motion
occurs at both the intercarpal and radiocarpal joints. The distal row flexes
and deviates ulnarly, whereas the proximal row extends and moves radially at
the radiocarpal joint.
The radial deviators of the wrist are
the extensor carpi radialis longus and
brevis, flexor carpi radialis, abductor
pollicis longus, and extensor pollicis
brevis. The ulnar deviators are the extensor carpi ulnaris and flexor carpi ulnaris, with the extensor carpi ulnar is
Figure 33
the elbow exe d without resistance; (2) supination w ith the elbow extende d without resistance; (3)
supination against resistance. +++ = maximum activity, ++ = mild activity, + = minimal ac tivity, − =
no activi ty. The supinator is the main supi nator. The biceps is the reser ve supinator, functioning b est
with the elbow exed 90° or when speed or power is required.
Schematic drawing demonstrates supination of the forearm. (1) Supination with
becoming more effective with forearm
pronation.
The degree of participation of the
digital motors determines recruitment
of the wrist motors. When the wrist is
in extension and the fingers make a soft
fist, the following wrist motors are active in descending order: extensor carpi
radialis brevis, extensor carpi ulnaris,
and extensor carpi radialis longus. With
a tight fist, all three extensors are maximally active18 (Figure 36). When the
fingers are gently extended and the wrist
is held in extension, the extensor carpi
ulnaris and flexor carpi ulnaris are active. The forceful opening of the fingers
brings into action, in descending order,
the following additional wrist motors:
extensor carpi radialis brevis, palmaris
longus, extensor carpi radialis longus,
and flexor carpi radialis18 (Figure 37).
Grip strength is maximal with the wrist
in 35° of extension and 7° of ulnar deviation and is substantially reduced when
the wrist deviates from this position.
13
Hand
Fingers
Located at the end of a multisegmented system, the hand functions within
the action envelope E3 of the wrist. The
flexing finger traces an action envelope, E4, that is an equiangular spiral19
(Figure 34). When the wrist is extend-
ed, the field of motion of the fingers is
within the wrist envelope E3. With wrist
flexion, the action envelope E4 of the fingers extends beyond the field of motion
of the wrist (Figure 34).
With prehension of the fingers, the
interphalangeal and metacarpophalangeal joints must flex in a coordinated
fashion to permit wrapping of the digital palmar surface over the surface of
Figure 34
wrist and E4 is the action envelope of the nger tracing an equiangular spiral. The eld of motion of the nger is within E3 when the wrist is extended
and projects proximally when the wrist is exed. B, The extended wrist, when rotated, explores the outer half of a circle that is the base of spheroid
E3. C, The exed wrist, when rotated, explores the inner half of a circle that is the base of spheroid E3.
Atlas of Amputations and Limb Deciencies, Fourth Edition © 2016 American Academy of Orthopaedic Surgeons
108
Schematic drawings showing wrist and hand motion. A, Field of motion of the wrist and hand, where E3 is the action envelope of the
Chapter 8: Kinesiology of the Upper Limb
Figure 35
the contribution of the radiocarpal and midcarpal joints to exion-extension. A, For exion, 60% is midcarpal and 40% is radiocarpal.
B, For extension, 33.5% is midcarpal and 66.4%
is radiocarpal. (Reproduced with permission
from Sarra an SK, Melamed JL, Goshgarian GM:
Study of wrist motion in exion and extension.
Clin Orthop Relat Res 1977; 126:153-159.)
Schematic drawings showing
the object. Separately, the distal joint
is flexed by the flexor profundus, the
middle joint by the flexor superficialis,
and the metacarpophalangeal joint by
the intrinsic muscles. The coordination
of flexion at the interphalangeal and the
metacarpophalangeal joints is brought
about by the instantaneous participation of the extrinsic-intrinsic motors
commanded by the motor cortex as
well as through passive restraints. This
passive restraint is primarily the result
of the oblique retinacular ligament that
arises from the palmar aspect of the
proximal phalanx and adjacent flexor
sheath, passing volar to the proximal
interphalangeal joint, lateral to the
middle phalanx, and dorsal to the distal interphalangeal joint, inserting into
the distal extensor hood. This ligament
coordinates flexion and extension at
the proximal interphalangeal and distal
interphalangeal joints.
Figure 36
sion (1) when making a soft st and (2) when making a tight st. +++ = maximum activity, ++ =
mild activity, + = minimal activity.
Figure 37
tension (1) when opening the ngers gently and (2) when opening the ngers forcefully. +++ =
maximum activity, ++ = mild activity, + = minimal activity.
A fine mechanism of coordination
is present locally in the fingers at the
level of the interphalangeal joints as initially presented by Landsmeer20 (Fig-
ure 38). Finger flexion is initiated at the
level of the distal interphalangeal joint
by the flexor digitorum profundus. As
the distal interphalangeal joint flexes,
the terminal tendon is displaced distally, causing distal movement of the
extensor trifurcation through pull of
the lateral slips, resulting in relaxation
of the central slip. Simultaneously, the
Schematic drawing demonstrates participation of the wrist motors in wrist exten-
Schematic drawing demonstrates participation of the wrist motors in wrist ex-
oblique retinacular ligament attached
to the terminal tendon also increases
in tension and, passing volar to the
axis of the proximal interphalangeal
joint, automatically flexes the middle
phalanx. This is a passive mechanism
of interphalangeal joint motion. When
the proximal interphalangeal joint is
flexed approximately 70°, the previously relaxed central slip develops tension,
pulling the extensor trifurcation farther
distally, relaxing the lateral slips, lateral conjoined tendon, and terminal
© 2016 American Academy of Orthopaedic Surgeons Atlas of Amputations and Limb Deciencies, Fourth Edition
109
Section 1: General Topics
Figure 38
strating Landsmeer’s concept of coordination
of interphalangeal joint exion. A, Finger in extension. B, Active exion at the distal interphalangeal joint increases tension in the terminal
extensor tendon and oblique retinacular ligament. Extensor trifurcation advances distally,
extensor central slip relaxes, and the middle
joint exes automatically to the same degree. C
and D, As exion continues, the middle slip increases in tension. Trifurcation advances more
distally, relaxing the lateral tendons and terminal tendon, including the oblique retinacular
ligament. The distal joint then exes without
encountering extensor resistance.
Schematic drawings demon-
tendon. This unloading of the terminal
tendon allows for complete flexion of
the distal interphalangeal joint without
encountering resistance from the extensor tendon. Any break in this system of
activation and coordination interferes
with the function of prehension.
The absence of intrinsic muscle action not only breaks the contour of the
longitudinal arch of the finger but also
creates an abnormal pattern of function.
The three joints flex successively from a
distoproximal direction rather than simultaneously, and this pattern of flexion
prevents the palmar skin from making
the necessary surface contact with the
object.
In the absence of resistance, the flexor digitorum profundus is the primary
Figure 39
strating the extensor system for the distal interphalangeal joint. 1 = terminal tendon, 2 =
middle slip, 3 = lateral slip, 4 = intrinsic tendon,
5 = quadrilateral lamina.
Schematic drawing demon-
finger flexor. However, when resistance
is encountered, the flexor digitorum superficialis becomes activated to assist in
proximal interphalangeal flexion and
the interossei become more responsible
for metacarpophalangeal flexion.
The opening of the fingers is an essential prerequisite for the act of prehension. As in finger flexion, extension
occurs through a complex interaction of
active and passive forces. Extension of
the metacarpophalangeal joint is con
trolled by the long extensor. Although
a direct connection between the extensor tendon and the proximal phalanx
is usually present, action at the metacarpophalangeal joint occurs primarily through two indirect mechanisms.
First, an indirect action is exerted in
conjunction with the flexor digitorum
superficialis.6 With the metacarpophalangeal and proximal interphalangeal
joints in full flexion, the initial pull of
the extensor acts on the middle phalanx
via the central slip. This force is transmitted through the proximal interphalangeal joint to the head of the proximal
phalanx, producing extension at the
metacarpophalangeal joint. The flexor
digitorum superficialis is necessary in
this action to prevent initial proximal
interphalangeal extension. Second, as
the metacarpophalangeal joint extends,
the sagittal bands migrate proximally,
over the metacarpophalangeal joint, allowing the pull of the extensor hood to
act through the sagittal bands on the
proximal phalanx, producing further
extension at the metacarpophalangeal
joint.
The proximal interphalangeal joint is
extended by the active force of the lumbricals and central slip of the long extensor. When the proximal interphalangeal
joint extends actively, the oblique retinacular is subjected to tension and automatically extends the distal joint.20 This
is another mechanism of coordination
on the extensor side of the finger. In
addition, the distal joint is extended by
the terminal tendon, which is formed
by the long extensor lateral slip but also
receives a contribution from the corresponding intrinsic tendons (Figure 39).
Lateral motion and rotation of the
fingers are determined by the intrinsic
muscles. The dorsal interossei abduct
or spread the fingers, whereas the volar
interossei adduct the fingers relative to
a functional axis passing through the
third metacarpal. There is more abduction to the finger in extension and less
-
in flexion because of the relative laxity
of the collateral ligaments in extension.
A final passive mechanism of flexion-extension of the finger is present through
a tenodesis effect: wrist extension flexes
the fingers, and wrist flexion extends
them.
Thumb
Motion of the thumb occurs through the
trapeziometacarpal, metacarpophalangeal, and interphalangeal joints. Flexion-extension motion occurs in the plane
parallel to the palm with flexion being
across the palm, toward the hypothenar eminence, and extension being away
from the palm. Extension has also been
Atlas of Amputations and Limb Deciencies, Fourth Edition © 2016 American Academy of Orthopaedic Surgeons
110
referred to as radial abduction. Abduction-adduction of the thumb occurs in
the plane perpendicular to the palm.
The thumb sweeps a conoid surface
through circumduction.21 This curved
surface is flattened on the palmar aspect
(Figure 40). All functional activities
of the thumb occur within this envelope. Through flexion-adduction, the
thumb traces the segment of the base
of the cone along the palmar surface.
The curve traced during this motion
is an equiangular spiral21 (Figure 41).
Through extension-abduction, the ray
returns to its initial position.
A fundamental function of the thumb
is opposition with the fingers that occurs
as the pad of the thumb is set against
the pad of a corresponding finger. To
bring about opposition, the thumb is
abducted in a plane perpendicular to the
palm and flexed and rotated (pronated)
on its long axis (Fig ure 42). The thumb
and the pad of the finger make contact
along the equiangular spiral curve of
the finger. This action involves motion
at all three articulations of the thumb,
with the carpometacarpal joint being
the most important. Overall, the carpometacarpal joint allows approximately
50° to 60° of flexion-extension, 40° to
45° of abduction-adduction, and 10° to
20° of axial rotation.
22
Opposition occurs in multiple stages
(Figure 42). First, the thumb is extended and supinated to open the first web
space. This is motored by the abductor
pollicis longus, extensor pollicis brevis,
and abductor pollicis brevis. In addition, the extensor pollicis longus acts
to extend (and hyperextend) the interphalangeal joint, bringing the thumb
tip farther from the palm. The thumb
is then sequentially abducted, flexed,
and pronated to position the tip against
the pad of a corresponding finger. This
action is determined by the abductor
pollicis brevis, opponens pollicis, and
the flexor pollicis brevis. In weak opposition, the action of the opponens
pollicis predominates.23 As the force
Chapter 8: Kinesiology of the Upper Limb
Figure 40
strating the eld of motion of the thumb. The
basic motions are: 1 to 2, extension and abduction in the palmar plane; 2 to 3, abduction in
the plane perpendicular to the palm with pronation; 3 to 4, exion, adduction, and further
pronation; 4 to 1, extension and palmar abduction with supination; 1 to 4, exion, adduction,
and pronation.
Figure 42
web space is opened by extension and supination of the thumb (a to b). The thumb is then abduc ted through curve 1 (b to c), bringing it perpendicular to the palm. Flexion (curve 2) and pronation
(curve 3) complete the motion, positioning the thumb tip against the tip of a corresponding nger
(c to d). B, In full opposition, the thumb tip is fully pronated, with the two nails nearly parallel and
opposite one another.
of opposition increases, flexor pollicis
brevis activity increases and exceeds
the opponens pollicis (Figure 43). In
forceful opposition to the ulnar digits,
the opponens pollicis becomes more
predominant and the adductor pollicis
becomes involved. As resistance increases, the extrinsic muscles are recruited.
Schematic drawing demon-
Figure 41
strates that the thumb traces an equiangular
spiral when sweeping the palmar surface from
A to B.
Schematic drawing demonstrates opposition of the thumb. A, Initially, the rst
Schematic drawing demon-
nonprehensile and prehensile activities.
The former includes touching, feeling,
pressing down with the fingers, tapping,
vibrating the cord of a musical instrument, lifting or pushing with the hand.
Prehensile activities are grouped into
precision and power grips.23 Precision
grip involves participation of the radial
side of the hand with the thumb, index,
Functional Activities
The functional activities of the hand
are extensive but can be grouped into
and middle fingers to form a three-jaw
chuck. When the pads of these digits
come into contact, the grip is described
© 2016 American Academy of Orthopaedic Surgeons Atlas of Amputations and Limb Deciencies, Fourth Edition
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