Chapter 5
Structure and Function of the Elbow
and Forearm Complex
Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
Osteology
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Four bones related to the function of the elbow and
forearm complex include:
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Scapula
Distal humerus
Ulna
Radius
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Scapula
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Coracoid process
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Supraglenoid tubercle
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Proximal attachment for the short head of the biceps
Proximal attachment for the long head of the biceps
Infraglenoid tubercle
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Marks the proximal attachment for the long head of the
triceps
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Distal Humerus
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Trochlea
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Spool-shaped structure located on the medial side of the
distal humerus that articulates with the ulna to form the
humeroulnar joint
Coronoid fossa
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Small pit located just superior to the trochlea that accepts
the coronoid process of the ulna when the elbow is fully
flexed
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Distal Humerus – cont’d
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Capitulum
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Lateral to the trochlea, articulates with the head of the radius
to form the humeroradial joint
Medial epicondyle
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Prominent bone projection on the distal humerus’ medial
side, serving as the proximal attachment for most wrist flexor
muscles, the pronator teres, and the medial collateral
ligament of the elbow
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Distal Humerus – cont’d
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Lateral epicondyle
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Medial and lateral supracondylar ridges
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Proximal attachment for most wrist extensor muscles,
supinator muscle, and lateral collateral elbow ligament
Immediately proximal to both epicondyles
Olecranon fossa
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Relatively deep, broad pit located on the posterior side of the
distal humerus
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Ulna
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Olecranon process
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Large, blunt, proximal tip of the ulna; rough posterior surface
is the distal attachment for the triceps muscles
Trochlear notch
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Large “jaw-like” curvature of the proximal ulna articulating
with the trochlea; inferior tip comes to a point, forming the
coronoid process
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Ulna – cont’d
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Coronoid process
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Radial notch
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Strengthens the articulation of the humeroulnar joint by firmly
“grabbing” the trochlea
Slightly inferior and lateral to the trochlear notch
Articulates with radial head to form the proximal radioulnar joint
Styloid process
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Pointed projection of bone that arises from the ulnar head
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Radius
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Radial head
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Shaped like wide disc on proximal end of radius
Superior surface consists of shallow, cup-shaped depression
called the fovea that articulates with the humeral capitulum,
forming the humeroradial joint
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Radius – cont’d
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Bicipital tuberosity (radial tuberosity)
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Styloid process
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Enlarged ridge of bone located on the anterior-medial aspect
of the proximal radius; primary distal attachment for the
biceps brachii
Pointed projection of bone off the distal lateral radius
Ulnar notch
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Small depression on the medial side of the distal radius that
articulates with the ulnar head
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Arthrology of the Elbow Complex
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Humeroulnar joint
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Provides most of elbow’s structural stability by trochlear
notch interlocking with trochlea
Limits motion of elbow to flexion and extension
Humeroradial joint
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Formed by capitulum articulating with fovea
Permits continuous contact between radial head and
capitulum during supination, pronation, flexion, and
extension
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Arthrology of the Elbow Complex – cont’d
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Normal cubitis valgus
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Natural outward angulation of the forearm within the frontal
plane
Called the “carrying angle” because of its function of keeping
a carried object away from the body
Elbow trauma can result in either excessive cubitus valgus
or cubitus varus
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Supporting Structures of the Elbow
Joint
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Articular capsule
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Thin, expansive band of connective tissue enclosing the
humeroulnar, humeroradial, and radioulnar joints
Medial collateral ligament
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Attaches proximally to the medial epicondyle and distally to
the medial aspects of the coronoid and olecranon processes;
provides stability by resisting cubitus valgus-producing
forces
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Supporting Structures
of the Elbow Joint – cont’d
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Lateral collateral ligament
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Originates on the lateral epicondyle and splits into two fiber
bundles known as the radial collateral ligament, which
attaches to the annular ligament, and the lateral (ulnar)
collateral ligament, which attaches to lateral aspect of the
proximal ulna
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Provides elbow stability by resisting cubitus varus–
producing forces
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Supporting Structures
of the Elbow Joint – cont’d
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Limits excessive varus and valgus deformations of
the elbow
Medial collateral ligament is most often injured,
during attempts to “catch” oneself from a fall
Because these ligaments also become taut at the
extremes of flexion and extension, these motions can
also damage the collateral ligaments
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Elbow Joint Kinematics
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Elbow flexion and extension occur in the sagittal
plane about a medial-lateral axis of rotation, which
courses through both epicondyles
Range of motion at the elbow normally spans from 5
degrees beyond extension to 145 degrees of flexion
Most activities use a more limited 100-degree arc of
motion, between 30 and 130 degrees of flexion
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Arthrology of the Forearm Complex
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Composed of the proximal and distal radioulnar joints
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Pronation and supination occur as a result of motion at each
of these two joints
Pronation and supination do not occur at the hand
Firm articulation between the distal radius and carpal
bones requires that the hand follows the rotation of
the radius
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Proximal and Distal Radioulnar
Joints: Supporting Structures
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Annular ligament
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Thick, circular band of connective tissue that wraps around
the radial head and attaches to either side of the radial notch
of the ulna
Holds the radial head firmly against the ulna, allowing it to
spin freely during supination and pronation
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Proximal and Distal Radioulnar
Joints: Supporting Structures – cont’d
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Distal radioulnar joint capsule
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Reinforced by palmar and dorsal capsular ligaments
Provides stability to the distal radioulnar joint
Interosseous membrane
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Helps bind the radius to the ulna
Serves as a site for muscular attachments and a mechanism
to transmit forces proximally through the forearm
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Forearm Complex Kinematics
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Supination occurs in many functional activities that
require the palm to be turned up
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e.g., holding a bowl of soup (“soup”-in-ation)
Pronation, in contrast, is involved with activities that
require the palm to be turned down
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e.g., pushing up from a chair
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Forearm Complex Kinematics – cont’d
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Supination and pronation occur as the radius rotates
around an axis of rotation that travels from the radial
head to the ulnar head
The 0 degree or neutral position of the forearm is the
thumb-up position
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From this position, normally 85 degrees of supination and 75
degrees of pronation occur
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Forearm Complex Kinematics – cont’d
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With the humerus fixed and forearm free, the
arthrokinematics of supination and pronation are as
follow:
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Radius moves; ulna stays stationary
Radial head spins in place, in the direction of the moving
thumb
Distal radius rolls and slides in the same direction relative to
the ulnar head
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Forearm Complex Kinematics – cont’d
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The arthrokinematics of pronation are essentially the
same as supination, except in reverse
During supination, the radial head spins in the
direction of the thumb
Spinning head of the radius also makes contact with
the capitulum of the humerus
At the distal radioulnar joint, the concave surface of
the distal radius rolls and slides in the same direction
across the stationary ulna
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Force Transmission through
the Interosseous Membrane
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Most interosseous membrane fibers are oriented 45
degrees from the long axis of the forearm, helping
transmit compressive forces from the hand to the
upper arm
Push-up actions create a compressive force passing
through the hand to the wrist, 80% of which is
transmitted through the radius at the radiocarpal joint
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Force Transmission through
the Interosseous Membrane – cont’d
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Proximal-directed force passes up radius and,
because of specific angulation of interosseous
membrane, is transferred partly to ulna
As a result, compressive force that enters distal
forearm at radius exits proximal forearm through both
humeroulnar and humeroradial joints and is
transferred up to shoulder
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Force Transmission through
the Interosseous Membrane – cont’d
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Direction and alignment of interosseous membrane
helps distribute force more evenly across elbow
If interosseous membrane were oriented 90 degrees
to its actual orientation, a compressive force directed
up through radius would slacken (rather than tense)
membrane
Slackened or loose membrane—like a loose
rope—cannot transmit a pull
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Muscles of the Elbow and
Forearm Complex: Innervation
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Musculocutaneous nerve
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Radial nerve
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Supplies most of the elbow flexors, except the
brachioradialis and pronator teres
Supplies all the muscles that extend the elbow
Median nerve
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Supplies all the pronators of the forearm
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Muscles of the Elbow and
Forearm Complex
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Prime movers of elbow flexion
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Biceps brachii, brachialis, and brachioradialis
Pronator teres is secondary elbow flexor
Biceps brachii, brachioradialis, and pronator teres
may also pronate or supinate forearm
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Elbow Flexors: Biceps Brachii
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Proximal attachment
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Distal attachment
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Long head: supraglenoid tubercle of scapula
Short head: coracoid process of scapula
Bicipital tuberosity of radius
Actions
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Elbow flexion
Forearm supination
Shoulder flexion
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Elbow Flexors: Brachialis
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Proximal attachment
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Distal attachment
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Coronoid process of ulna
Innervation
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Anterior aspect of distal humerus
Musculocutaneous nerve
Actions
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Elbow flexion
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Elbow Flexors: Brachioradialis
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Proximal attachment
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Distal attachment
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Lateral supracondylar ridge of humerus
Near styloid process of distal radius
Innervation: radial nerve
Actions
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Elbow flexion
Pronating or supinating the forearm to neutral (thumb-up)
position
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Functional Considerations:
Biceps vs. Brachialis
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Nervous system selects just the “right” muscle and
optimal amount of force for specific task
Brachialis is muscle of choice for most elbow flexion
activities
If flexion movement requires a strong supination
component, nervous system would find it necessary
to also recruit biceps muscle
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Elbow Extensors: Triceps Brachii
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Proximal attachment
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Long head: infraglenoid tubercle of scapula
Lateral head: posterior aspect of the superior humerus, lateral to
radial groove
Medial head: Posterior aspect of the superior humerus, medial to
radial groove
Distal attachment―olecranon process of ulna
Innervation―radial nerve
Actions
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Elbow extension
Shoulder extension—long head only
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Elbow Extensor: Anconeus
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Proximal attachment
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Distal attachment
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Olecranon process of ulna
Innervation
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Posterior aspect of lateral epicondyle of humerus
Radial nerve
Actions
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Elbow extension
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Functional Considerations:
One- vs. Two-Joint Muscles
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Functions that require large forces for extending the
elbow usually demand strong activation of all three
heads of triceps and anconeus
Many daily functions require relatively low elbow
extension force, requiring nervous system to activate
only one-joint extensor muscles
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Supinators
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Primary supinator muscles are biceps brachii and
supinator muscle
Secondary supinator muscles include the extensor
pollicis longus and the extensor indicis
Brachioradialis can supinate or pronate forearm to
mid position
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Supinator
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Proximal attachment
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Distal attachment
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Lateral surface of the proximal radius
Innervation
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Lateral epicondyle of humerus and supinator crest of ulna
Radial nerve
Actions
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Forearm supination
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Functional Considerations:
Interaction of Supinator Muscles
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Contraction of biceps brachii from a pronated position
can effectively spin radius in direction of supination
Effectiveness of biceps as supinator is greatest when
elbow is flexed to near 90 degrees
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Functional Considerations: Interaction
of Supinator Muscles – cont’d
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At 90-degree elbow position, biceps tendon
approaches radius at 90-degree angle
Similar to pulling string attached to toy top or yo-yo,
linear force immediately produces rotation and
therefore efficiently rotates radius
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Pronators: Pronator Teres
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Proximal attachment
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Humeral head: medial epicondyle of humerus
Ulnar head: just medial to tuberosity of ulna
Distal attachment: lateral surface of mid radius
Innervation: median nerve
Actions
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
Forearm pronation
Elbow flexion
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Pronators: Pronator Quadratus
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Proximal attachment
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Distal attachment
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Anterior surface of distal radius
Innervation
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Anterior surface of distal ulna
Median nerve
Actions

Forearm pronation
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Functional Considerations: Interaction
of the Pronator Muscles
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Pronator teres muscle assists pronator quadratus
muscle when larger pronation forces are required or
when elbow flexion is also desired
If pronator teres is activated, elbow will also flex
unless neutralized by triceps muscles
Relationship is similar to that of supinator and biceps
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Summary
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Elbow and forearm complex contributes highly to
overall function of upper extremity
Located between shoulder and hand, muscles must
stabilize region to allow for transmission of external
forces between shoulder and hand
Structure of four joints of elbow and forearm complex
allows for both mobility and stability needs
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