Elbow Joint - Biomech.
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ELBOW COMPLEX
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INTRODUCTION The elbow complex includes the elbow joint (humeroulnar and
humeroradial joints) and the proximal and distal radioulnar joints.
The elbow joint is considered to be a compound joint that functions as a
modified or loose hinge joint.
One degree of freedom is possible at the elbow, permitting the motions
of flexion and extension, which occur in the sagittal plane around a
coronal axis. A slight bit of axial rotation and side-to-side motion of the
ulna occurs during flexion and extension, and that is why the elbow is
considered to be a modified or loose hinge joint rather than a pure
hinge joint.
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Two major ligaments and five muscles are directly
associated with the elbow joint.
Three of the muscles are flexors that cross the anterioraspect of the joint.
The other two muscles are extensors that cross the
posterior aspect of the joint.
The proximal and distal radioulnar joints are linked and
function as one joint. The two joints acting together
produce rotation of the forearm and have 1 degree of
freedom of motion.
The radioulnar joints are diarthrodial uniaxial joints of
the pivot (trochoid) type and permit rotation
(supination and pronation), which occurs in the
transverse plane around a longitudinal axis.
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Six ligaments and four muscles are associated
with these joints. Two muscles are for
supination, and two are for pronation.
The elbow joint and the proximal radioulnar jointare enclosed in a single joint capsule but
constitute distinct articulations.
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ELBOW JOINT - ARTICULATION
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ARTICULATION HUMERORADIAL &
HUMEROULNAR JOINTS
The articulating surfaces on the anterior aspect of the distal
humerus are the hourglass-shaped trochlea and the spherical
capitulum.
These structures are situated between the medial and lateralhumeral epicondyles.
The trochlea, which forms part of the humeroulnar articulation, is
set at an angle on the medial aspect of the distal humerus and
lies slightly anterior to the humeral shaft.
A groove called the trochlear groove spirals obliquely around the
trochlea and divides it into medial and lateral portions.
The medial portion of the trochlea projects distally more than thelateral ortion and results in a val us an ulation of the forearm.
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The indentation in the humerus located just
above the trochlea is called the coronoid fossa
and is designed to receive the coronoid processof the ulna at the end of elbow flexion range of
motion (ROM).
The capitulum, which is part of the humeroradialarticulation, is located on the anterior lateral
surface of the distal humerus.
The capitulum, like the trochlea, lies anterior tothe shaft of the humerus. A groove called the
capitulotrochlear groove separates the
capitulum from the trochlea.
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The indentation located on the humerus just
above the capitulum is called the radial fossa
and is designed to receive the head of the radius
in elbow flexion.
Posteriorly, the distal humerus is indented by a
deep fossa called the olecranon fossa, which is
designed to receive the olecranon process of the
ulna at the end of elbow extension ROM.
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ARTICULATING SURFACES OF RADIUS
AND ULNA The articulating surfaces of the ulna and radius
correspond to the humeral articulating surfaces.
The ulnar articulating surface of the humeroulnarjoint is a deep semicircular concave surface called
the trochlear notch.
The proximal portion of the notch is divided intotwo unequal parts by the trochlear ridge, whichcorresponds to the trochlear groove on thehumerus.
The ulnar coronoid process forms the distal end ofthe notch, whereas the olecranon process projectsover the proximal end.
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The radial articulating surface of the
humeroradial joint is composed of the proximal
end of the radius, known as the head of theradius.
The radial head has a slightly cup-shaped
concave surface called the fovea that issurrounded by a rim.
The radial heads convex rim fits into the
capitulotrochlear groove.
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ARTICULATION
Articulation between the ulna and humerus at the
humeroulnar joint occurs primarily as a sliding
motion of the ulnar trochlear ridge on the humeral
trochlear groove.In extension, sliding continues until the olecranon
process enters the olcranon fossa .
In flexion, the trochlear ridge of the ulna slides alongthe trochlear groove until the coronoid process
reaches the floor of the coronoid fossa in full flexion.
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Articulation between the radial head and the
capitulum at the humeroradial joint involves
sliding of the shallow concave radial head overthe convex surface of the capitulum.
In full extension, no contact occurs between the
articulating surfaces. In flexion, the rim of the radial head slides in the
capitulotrochlear groove and enters the radial
fossa as the end of the flexion range is reached.
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JOINT CAPSULE
The humeroulnar and humeroradial joints and thesuperior radioulnar joint are enclosed in a single jointcapsule.
Anteriorly, the proximal attachment of the capsule is
just above the coronoid and radial fossae,and distallyit is inserted into the ulna on the margin of thecoronoid process.
The capsule blends with the proximal border of the
annular ligament except posteriorly, where thecapsule passes deep below the annular ligament toattach to the posterior and inferior margins of theneck of the radius
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Laterally, the capsules attachment to the radius
blends with the fibers of the lateral collateral
ligament (LCL).
Medially, the capsule blends with fibers of the
medial collateral ligament (MCL).
Posteriorly, the capsule is attached to the
humerus along the upper edge of the olecranon
fossa.
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The capsule is fairly large, loose, and weak
anteriorly and posteriorly, and it contains folds
that are able to unfold to allow for a full range of
elbow motion.
Laterally and medially, the capsule is reinforced
by the collateral ligaments.
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LIGAMENTS
The two main ligaments associated with the
elbow joints are the
medial (ulnar) and
lateral (radial) collateral ligaments.
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MEDIAL COLLATERALLIGAMENT
The MCL is considered to be the major soft tissuerestraint of valgus stress at the medial aspect of
the elbow.
The elbow joints normal valgus configuration
subjects the medial aspect of the joint to a high
degree of valgus stress, especially during
throwing and golfing activities. The MCL is described as consisting of two parts
(anterior and posterior)or three parts (anterior,
oblique or transverse, and posterior).
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The anterior part of the MCLextends from the
anterior aspect, tip, and medial edge of the
medial epicondyle of the humerus to attach on
the ulnar coronoid process.
Mechanoreceptors (Golgi organs, Ruffini
terminals, Pacini corpuscles, and free nerve
endings) are densely distributed near the
ligaments humeral and ulnar attachments.
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The anterior portion of the MCL is considered to
be the primary restraint of valgus stress from 20
to 120 degrees of elbow flexion.
Scientists the composition of the anterior portion
of the MCL as having an anterior band and a
posterior band that tighten in a reciprocalmanner as the elbow flexes and extends.
The anterior band of the anterior portion was
found by these authors to be the primaryrestraint of valgus at 30, 60, and 90 degrees of
flexion.
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The posterior portion of the MCL extends from
the posterior aspect of the medial epicondyle of
the humerus to attach to the ulnar coronoid and
olecranon processes.
The posterior MCLlimits elbow extension but
plays a less significant role than the anterior MCL
in providing valgus stability for the elbow.
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The oblique (transverse) fibers of the MCL
extend between the olecranon and ulnar
coronoid processes.
This portion of the ligament assists in providingvalgus stability and helps to keep the joint
surfaces in approximation.
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LATERAL COLLATERALLIGAMENT
The lateral collateral ligamentous complex
includes the LCL, the lateral ulnar collateral
ligament (LUCL)and the annular ligament.
The LCL is a fan-shaped structure that extends
from the inferior aspect of the lateral epicondyleof the humerus to attach to the annular ligament
and to the olecranon process.
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LUCL - Ligamentous tissue extending from the
lateral epicondyle to the lateral aspect of the
ulnar and the annular ligament, adheres closely
to the supinator, extensor, and anconeus muscles
and lies just posterior to the LCL.
Function ofLCL
1. stabilizes elbow against varus torque.
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2. stabilizes against combined varus and supination
torques.
3. reinforces humeroradial joint and assists in
providing some resistance to longitudinal
distraction of the articulating surfaces.
4. stabilizes radial head, thus providing a stable
base for rotation.
5. maintains posterolateral rotatory stability.
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6. prevents subluxation of humeroulnar joint by
securing ulna to humerus.
7. prevents forearm from rotating off of thE
humerus in valgus and supination during flexionfrom fully extended position.
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MUSCLES
Nine muscles cross the anterior aspect of theelbow joint.
3 have primary functions at the elbow :
B
rachialisBiceps brachii
Brachioradialis
Major functions at radioulnar joints :Supinator
Pronator teres
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Remaining muscles have primary functions at the
wrist, hand & finger joints but are considered to
be weak flexors at the elbow :
Flexor carpi radialis
Flexor carpi ulnaris
F
lexor digitorum superficialis
Palmaris longus
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The two extensors of the elbow are :
Triceps
Anconeus
In addition to the anconeus muscle, a number of
muscles with primary actions at the wrist and
fingers :
Extensor carpi radialis longus (ECRL)
Extensor carpi radialis brevis (ECRB)
Extensor digitorum communis (EDC)
Extensor carpi ulnaris (ECU)
Extensor digiti minimi (EDM)
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The ECRL, ECRB, and ECU are active in gripping ,
hammering, and sawing activities. Therefore, the
repetitive pull of these muscles during a patientsworkday could injure the common extensor
tendon.
The types of changes that might be seen in eithera patients tendon or his muscle, from
examinations of biopsy material from patients
with chronic lateral elbow pain diagnosed as
lateral epicondylitis (inflammation of the lateral
epicondyle and surrounding tissues).
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ELBOW JOINT FUNCTION AXIS OF
MOTION
An exact determination of the axis of motion at
the elbow is important because of the need to
position elbow prostheses in such a way that
they correctly mimic elbow joint motion.
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Screw displacement axis (SDA)
Screw displacement axes (SDAs) are used to
define the elbow axis accurately for proper
prosthesis positioning.
Location of the SDA is influenced by :
The type of flexion motion (active or passive)
By forearm position (pronation or supination)
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Intraindividual and interindividual variations in
the axes appear to be greater in the frontal
plane than in the horizontal plane.
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LONG AXIS OF THE HUMERUS &
FOREARM
In the anatomic position, the long axis of the
humerus and the long axis of the forearm
form an acute angle medially when they meet
at the elbow.
This normal valgus angulation is called the
carrying angle or cubitus valgus
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The average angle in full elbow extension is about 15
degrees.
An increase in the carrying angle beyond the average
is considered to be abnormal, especially if it occurs
unilaterally.
Normally, the carrying angle disappears when the
forearm is pronated and the elbow is in fullextension and when the supinated forearm is flexed
against the humerus in full elbow flexion.
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RANGE OF MOTION
A number of factors determine the amount of
motion that is available at the elbow joint. These
factors include :
The type of motion (active or passive),
The position of the forearm (relative pronation-supination).
Position of the shoulder.
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Type of motion (active/passive)
The range of active flexion at the elbow is usually
less than the range of passive motion, because
the bulk of the contracting flexors on the anterior
surface of the humerus may interfere with the
approximation of the forearm with the humerus.
Active flexion 135-145 degrees
Passive flexion 150-160 degrees
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Position of forearm (pronation/supination)
When the forearm is either in pronation or midprone
position, the ROM is less than it is when the forearm
is supinated.
Position of shoulder
Two joint muscles, such as the biceps brachii and the
triceps, that cross both the shoulder and elbowjoints may limit ROM at the elbow if a full ROM is
attempted at both joints simultaneously.
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The elbow has inherent articular stability at the
extremes of extension and flexion.
In full extension, the humeroulnar joint is in a
close-packed position. In this position, bony
contact of the olecranon process in the
olecranon fossa limits the end of the extension
range, and the configuration of the jointstructures helps provide valgus and varus
stability.
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Approximation of the coronoid process with the
coronoid fossa and of the rim of the radial head
in the radial fossa limits extremes of flexion.
S
welling and or pain also may limit the range ofelbow motion.
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MUSCLES OF ELBOW JOINT
Factors Affecting Elbow Muscle Activity :
Number of joints crossed by the muscle (one joint
or two joint muscles)
Physiologic cross-sectional area (PCSA)
Location in relation to joint
Position of the elbow and adjacent joints
Position of the forearm
Magnitude of the applied load
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Type of muscle action (concentric, eccentric,
isometric, isokinetic)
Speed of motion (slow or fast)
Moment arm (MA) at different joint positions
Fiber types
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Elbow Flexors
BRACHIA
LIS
Brachialis is considered to be a mobility muscle
because its insertion is close to the elbow joint
axis. It has a large strength potential.
Its MA is greatest at slightly more than 100
degrees of elbow flexion, at which its ability to
produce torque is greatest.
Because the brachialis is inserted on the ulna, it
is unaffected by changes in the forearm position
brought about by rotation of the radius.
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Being a one-joint muscle, it is not affected by the
position of the shoulder.
It also is active in all types of contractions
(isometric, concentric, and eccentric) during slow
and fast motions.
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BICEPSBRACHII
Also considered to be a mobility muscle because
of its insertion close to the elbow joint axis.
The long head of the biceps brachii has the
largest volume among the flexors.
The MA of the biceps is largest between 80 and
100 degrees of elbow flexion and, therefore, the
biceps is capable of producing its greatest torque
in this range.
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The MA of the biceps is rather small when the elbow
is in full extension, therefore, when the elbow is fully
extended, the biceps is less effective as an elbow
flexor than when the elbow is flexed to 90 degrees.
When the elbow is flexed beyond 100 degrees, the
translatory component of the muscle force is
directed away from the elbow joint and, therefore,
acts as a distracting or dislocating force.
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The functioning of the biceps is affected by the
position of the shoulder, if full flexion of theelbow is attempted with the shoulder in full
flexion, especially when the forearm is
supinated, the muscles ability to generate
torque is diminished.
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BRACHIORADIALIS
The brachioradialis is inserted at a distance from the
joint axis, and therefore the largest component of
muscle force goes toward compression of the joint
surfaces and hence toward stability.
The peak MA for the brachioradialis occurs between
100 and 120 degrees of elbow flexion.
The brachioradialis does not cross the shoulder
therefore unaffected by position of the shoulder.
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The position of the elbow joint was found to
affect brachioradialis muscle activity only duringvoluntary maximum eccentric contractions.
Elbow joint angle had no effect on concentric,
isometric, or isokinetic maximum voluntary
contractions.
The brachioradialis showed high levels of activity
during rapid alternating supination/pronation
motions.
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OTHER MUSCLES
The pronator teres, as well as the palmaris
longus, flexor digitorum superficialis, flexor carpi
radialis, and flexor carpi ulnaris, is a weak elbow
flexor with primary actions at the radioulnar and
wrist joints.
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Elbow extensors
The effectiveness of the triceps as a whole is
affected by changes in the position of the elbow
but not by changes in position of the forearm,
because the triceps attaches to the ulna and not
the radius.
Maximum isometric torque generation is at a
position of 90 degrees of elbow flexion.
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The triceps is active eccentrically to control
elbow flexion as the body is lowered to the
ground in a push-up.
The triceps is active concentrically to extend the
elbow when the triceps acts in a closed
kinematic chain, such as in a push-up.
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Superior & inferior radioulnar joints
The articulating surfaces of the proximal
radioulnar joint include the ulnar radial notch,
the annular ligament, the capitulum of thehumerus, and the head of the radius.
The articulating surfaces of the distal radioulnar
joint include the ulnar notch of the radius, the
articular disk, and the head of the ulna.
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Articular disk The articular disk is sometimes referred to as
either the triangular fibrocartilage (TFC) because
of its triangular shape or as a part ofthe
triangular fibrocartilage complex (TFCC) because
of its extensive fibrous connections.
The base of the articular disk is attached to the
distal edge of the ulnar notch of the radius.
The apex of the articular disk has twoattachments. One attachment is to the fovea on
the ulnar head. The other attachment is to the
base of the ulnar styloid process.
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The margins of the articular disk are thickened and
are either formed by or are integral parts of the
dorsal and palmar capsular radioulnar ligaments. 80% of the central portion of the articular disk is
avascular, in comparison with the peripheral area,
which was only 15% to 20% avascular.
The articular disk has two articulating surfaces:
The proximal (superior) surface and the distal
(inferior) surface.
The proximal surface of the disk articulates with theulnar head at the distal radioulnar joint, whereas the
distal surface articulates with the carpal bones as
part of the radiocarpal joint.
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RADIOULNAR ARTICULATION
The proximal and distal radioulnar joints are
mechanically linked; therefore, motion at one joint is
always accompanied by motion at the other joint.
The distal radioulnar joint is also considered to be
functionally linked to the wrist in that compressive
loads are transmitted through the distal radioulnar
joint from the hand to the radius and ulna.
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Pronation of the forearm occurs as a result of the
radiuss crossing over the ulna at the superioR
radioulnar joint.
Joint surface contact is optimal only with the
forearm in a neutral position between supination
and pronation.
In maximal pronation and supination, the
articulating surfaces have only minimal contact
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LIGAMENTS OF RADIOULNAR JOINTS
The three ligaments associated with the proximalradioulnar joint are the :
annular ligament
quadrate ligament
oblique cord
ANNULAR
LIGAM
ENT
The annular ligament is a strong band that forms
four fifths of a ring that encircles the radial head.
h l b d f h l l
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The proximal border of the annular ligament
blends with the joint capsule, and the lateral
aspect is reinforced by fibers from the LCL.QUADRATELIGAMENT
The quadrate ligament extends from the inferior
edge of the ulnas radial notch to insert in theneck of the radius.
Reinforces the inferior aspect of the joint capsule
and helps maintain the radial head in apposition
to the radial notch.
The quadrate ligament also limits the spin of the
radial head in supination and pronation.
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OBLIQUE CORD
The oblique cord is a flat fascial band on the
ventral forearm that extends from an attachmentjust inferior to the radial notch on the ulna to
insert just below the bicipital tuberosity on the
radius. May assist in preventing separation of the radius
and ulna.
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The dorsal and palmar radioulnar ligaments, as well
as the IOM, which stabilizes both proximal and distal
joints, reinforce the distal radioulnar joint.
The dorsal and palmar ligaments are formed by
longitudinally oriented collagen fiber bundles
originating from the dorsal and palmar aspects of
the ulnar notch of the radius.
The two ligaments extend along the margins of thearticular disk to insert on the ulnar fovea and base of
ulnar styloid process.
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The interosseous membrane (IOM), which is
located between the radius and the ulna, is acomplex structure consisting of the following
three components:
a central band,
a thin membranous portion, and
a dorsal oblique cord
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The central band is described as being a strong,
thick, ligamentous, or tendinous structure consisting
of bundles of fibers that run obliquely from the
radius to the ulna.
The central band has a very high collagen content.
In contrast to the central band, the membranous
portion is described as a soft and thin structure that
lies adjacent proximally and distally to the central
band.
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The dorsal oblique cord is considered to be part
of the IOM and should not be confused with the
oblique cord located on the ventral aspect of the
forearm, which is not considered to be part of
the IOM.
The dorsal oblique cord extends from the
proximal quarter of the ulna to the middle region
of the radius.
MUSCLE OF RADIOULNAR JOINTS
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MUSCLE OF RADIOULNAR JOINTS
The primary muscles associated with the
radioulnar joints are the
pronator teres,
pronator quadratus,
biceps brachii, and
supinator.
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FUNTION RADIOULNAR JOINT
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FUNTION RADIOULNAR JOINT
AXIS OF MOTION
The axis of motion for pronation and supination is
a longitudinal axis extending from the center ofthe radial head to the center of the ulnar head.
In supination, the radius and ulna lie parallel to
one another, whereas in pronation, the radius
crosses over the ulna.
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RANGE OF MOTION
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RANGE OF MOTION
The ROM of pronation and supination is assessed
with the elbow in 90 of flexion.
This position of the elbow stabilizes the humerus
so that radioulnar joint rotation may be
distinguished from rotation that is occurring at
the shoulder joint.
MUSCLE ACTION
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MUSCLE ACTION
1. The pronator teres has its major action at the
radioulnar joints.
Contributes some of its force toward stabilization of
the proximal radioulnar joint.
2. The pronator quadratus, a one-joint muscle, is
unaffected by changing positions at the elbow.
Active in unresisted and resisted pronation and in
slow or fast pronation.
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Pronators were found to be most efficient around
the neutral position of the forearm when the
elbow was flexed to 90 degrees.
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3. The supinator muscle may act alone during
unresisted slow supination in all positions of the
elbow or forearm.
The supinator also can act alone during unresisted fast
supination when the elbow is extended.
4. Activity of the biceps is always evident when
supination is performed against resistance and
during fast supination when the elbow is flexed to 90
degrees.
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The biceps has been found to exert four times as
much supination torque with the forearm in thepronated position than in other forearm
positions.
5. The anconeus muscle is active in supination and
pronation, and an elbow stabilization role has
been suggested to explain this activity.
STABILITY RADIOULNAR JOINT
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STABILITY RADIOULNAR JOINT
The ulnar head of the pronator teres may help bybinding the ulna to the radius while the humeral
head depresses the ulna during pronation.
The deep head of the pronator quadratus is active
throughout supination and pronation and therefore
is thought to provide dynamic stabilization for the
distal radioulnar joint.
A ti it i th ECU l t d i f
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Activity in the ECUmuscle exerts a depressive force
on the dorsal aspect of the ulnar head as the tendon
is stretched over the head during supination.
Tension in the tendon helps to maintain the position
of the ulnar head during both supination and
pronation.
The ECRBappears to act both as a stabilizer to the
forearm for gripping during pronation torques
(depending on forearm angle) and as a prime mover
for wrist extension for supination torques.
Th d l di l li t b t t i
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The dorsal radioulnar ligament becomes taut in
pronation, whereas the palmar radioulnar
ligament becomes taut in supination.
Radioulnar ligaments are able to prevent
separation of the radius from the ulna during
loading and also allow for force transmission
from the radius to the ulna through the distal
radioulnar joint.
Th ll i l 5 f l b h
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They allow approximately 5 mm of play between the
radius and ulna before providing resistance to
further distraction.
The radioulnar ligaments, the articular disk, and the
pronator quadratus maintain the ulna within the
ulnar notch and prevent the ulna from subluxating
or dislocating.
However, these ligaments allow a high degree of
mobility.
Th IOM id t bilit f th di t l j i t b
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The IOMprovides stability for the distal joint by
binding the radius and ulna together.
IOM in combination with the triangular
fibrocartilaginous complex provide important
longitudinal stabilization.
When the elbow was in the varus position (no
contact between the radial head and capitulum),
force was transmitted from the distal radius through
the IOM to the proximal ulna.
Wh th lb i th l iti
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When the elbow was in the valgus position
(contact between the radial head and the
capitulum), the force was transmitted through
the radius.
The articular disk acts as a cushion in allowing
compression force transmission from the carpals
to the ulna and acts as a stabilizer of the ulnar
side of the carpals.
MOBILITY & STABILITY ELBOW
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COMPLEX
FUNCTIONAL ACTIVITIES
A total arc of about 100 degrees of elbow flexion
(between 30 and 130) and about 100 degrees of
forearm rotation (50 supination and 50
pronation) is sufficient to accomplish simpletasks such as eating, brushing hair, brushing
teeth, and dressing.
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Using the telephone requires the largest arc of
motion in both flexion (92.8) and pronation and
supination (63.5).
Cutting with a knife requires the smallest arc of
flexion and of pronation/supination.
RELATIONSHIP OF THE HAND & WRIST
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RELATIONSHIP OF THE HAND & WRIST
The complete separation of the ulna from thecarpals by the articular disk and the formation of
a true diarthrodial joint lined with articular
cartilage are features that permit pronation and
supination to occur in every position of the hand
to the forearm.
Anatomically the hand and wrist muscles help
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Anatomically, the hand and wrist muscles help
reinforce the elbow joint capsule and contribute
to stability of the elbow complex.
The importance of compression or stabilization
of the elbow is that both the humeroradial and
humeroulnar articulations are subjected to
compressive forces during pulling activities and
that the MCL is heavily loaded.
EFFECTS OF AGE AND INJURY
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EFFECTS OFAGEAND INJURY
Age
Decrease in muscle strength with increasing age.
Injury
Injuries to the elbow are fairly frequent, and in
early adolescence the elbow is one of the mostcommon sites for apophysitis or strains at the
apophysis.
Compression Injuries
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Compression Injuries
Resistance to longitudinal compression forces at the
elbow is provided for mainly by the contact of bony
components; therefore, excessive compression
forces at the elbow often result in bony failure.
Falling on the hand when the elbow is in a close-
packed (extended) position may result in the
transmission of forces through the bones of the
forearm to the elbow.
If the forces are transmitted through the radius as may
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If the forces are transmitted through the radius, as may
happen with a concomitant valgus stress, a fracture of the
radial head may result from impact of the radial head on
the capitulum.
If the force from the fall is transmitted to the ulna, a
fracture of either the coronoid or olecranon processes
may occur from impact of the ulna on the humerus.
Ifneither the radius nor the ulna absorbs the excessive
force by fracturing, then the force may be transmitted to
the humerus and may result in a fracture of the
supracondylar area.
M l t ti l hi h
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Muscle contractions also may cause high
compression forces at the elbow.
Repetitive forceful contractions of the flexor carpi
ulnaris muscle may compress the ulnar nerve as it
passes through the cubital tunnel resulting in
cubital tunnel syndrome in which motion of the
fourth and fifth fingers is impaired.
Distraction Injuries
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Distraction Injuries
A tensile force of sufficient magnitude exerted on
a pronated and extended forearm may cause the
radius to be pulled inferiorly out of the annular
ligament. This injury is common in young
children younger than 5 years.
The injury is referred to as either nursemaids
elbow or pulled elbow.
Varus/Valgus Injuries
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If one side of the joint is subjected to abnormal
tensile stresses, the other side is subjected to
abnormal compressive forces.
The MCL is subjected to tensile stress during the
backswing or cock-up portion of throwing a ball.
If the stress on the MCL is repetitive, such as in
baseball pitching, the ligament may become lax and
unable to reinforce the medial aspect of the joint.
The resulting medial instability may cause anincrease in the normal carrying angle and excessive
compression on the lateral aspect of the joint so
that the radial head impacts on the capitulum.
If the abnormal compression forces on the
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If the abnormal compression forces on the
articular cartilage are prolonged, these forces
may interfere with the blood supply of thecartilage and result in avascular necrosis of the
capitulum.
The classic tennis elbow (epicondylitis of the
lateral epicondyle) appears to be caused by
repeated forceful contractions of the wrist
extensors, primarily the ECRB.
The tensile stress created at the origin of theECRB may cause microscopic tears that lead to
inflammation of the lateral Epicondyle.
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