Describes the biomechanics of elbow and injuries associated with them

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2. BIOMECHANICS OF ELBOW
COMPLEX
LECTURE-3
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3. Elbow biomechanics
 ROM flexion and extension - 0 to 140
 30 to 130 required for most ADL
 flexion-extension axis - a loose hinge.
 The active ROM for elbow flexion with the
forearm supinated is typically considered to
be from about 135 to 145 degrees.
 the range for passive flexion is between
150and 160.
 the forearm is either in pronation or midway
between supination and pronation, the ROM
is less than it is when the forearm is
supinated.
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 Passive tension in the triceps may limit elbow
flexion when the shoulder is simultaneously
moved into full flexion
 Passive tension created in the long head of the
biceps brachii by passive shoulder
hyperextension may limit full elbow extension

5. Axis of forearm motion.
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6. Axis of motion:
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 Variation of the flexion axis throughout ROM
described in terms of the screw displacement axis
(SDA), which shows the instantaneous rotation and
position of the axis throughout flexion.
 The average SDA - shown to be in line with the
anteroinferior aspect of the medial epicondyle, the
center of the trochlea, and the center projection of the
capitellum.

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 Variations
 activity of the various muscles may influence the
pattern of motion during active flexion,
 differences in contours of the joint surfaces may
explain differences during passive motion.

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 valgus-varus laxity was greatest between 0 and
40 of flexion and decreased considerably when
flexion exceeded 100.

10. Carrying angle:
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 The average angle in full elbow extension is
about 15
 This normal valgus angulation is called the
carrying angle or cubitus valgus.
 A varus angulation at the elbow is referred to as
cubitus varus
 the carrying angle disappears when the forearm
is pronated and the elbow is in full extension
 and when the supinated forearm is flexed against
the humerus in full elbow flexion.

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 The configuration of the trochlear groove
determines the pathway of the forearm during
flexion and extension.
 In the most common configuration of the groove,
the ulna is guided progressively medially from
extension to flexion, so that in full flexion, the
forearm comes to rest in the same plane as the
humerus.
 In extension, the forearm moves laterally until it
reaches a position slightly lateral to the axis of the
humerus in full extension.

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14. Pronation-supination
 The radiohumral and proximal radioulnar joints
 The normal range of forearm rotation is 180 with
 pronation of 80 to 90 and
 supination of ~ 90
 Most ADL can be accomplished with 100 of
forearm rotation
 (50 of pronation and 50 of supination)
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15. cont
 The normal axis of forearm rotation -
 the center of the radial head to the center of the
distal ulna
 axis of rotation shifts slightly ulnar and volar
during supination
 shifts radial and dorsal during pronation
 The radius moves
 proximally with pronation
 distally with supination
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16. Axis of forearm motion.
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17. cont
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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.
 Bony contact of the olecranon process in the olecranon
fossa limits the end of the extension range,
 configuration of the joint structures helps provide valgus
and varus stability.
 Resistance to valgus stress in extension:
 The bony components, MCL, and anterior joint capsule.
 Resistance to varus stress in full extension,
 lateral collateral complex and joint capsule.( half)
 The bony component (half).

18. cont
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 Resistance to joint distraction in the extended
position is provided entirely by soft tissue
structures.
 Anterior portion of the joint capsule provides the
majority of the resistance to anterior displacement
of the distal humerus out of the olecranon fossa,
whereas the MCL and LCL contribute only
slightly.
 Elbow flexion of about 80is considered to be the
elbow position at which the least amount of
tension is present in the joint capsule

19. Stability of elbow with rotation
 Forearm rotation - important role in stabilizing the
elbow, especially when the elbow is moved
passively.
 With passive flexion, the MCL deficient elbow is
more stable in supination.
 LCL-deficient elbow is more stable in pronation.
.
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21.  Most simple elbow dislocations - relatively stable
once reduced
 MCL is completely ruptured in nearly all cases.
 LCL is disrupted in most cases
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22. Joint forces
 significant compressive and shear forces at the elbow
 Loads across the elbow - distributed
 43% across the ulnohumeral joint and
 57% across the radiocapitellar joint
 Force transmission at the radiocapitellar joint is greatest
between 0 and 30 of flexion and is greater in pronation than in
supination.
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23. Muscles
 Muscles that cross the elbow joint act as
 dynamic stabilizers as they compress the
joint.
 Compression of the elbow joint by the
muscles protects the soft tissue constraints.
 throwing an object can cause a valgus stress
that is greater than the failure strength of the
MCL.
 The flexor-pronator muscle group contracts
during the throwing motion and provides
dynamic stabilization to the medial aspect of
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24. Muscles
 Elbow flexors
 Biceps brachii
 Brachialis
 Brachioradialis
 Weak assistance from Pronator teres
 Elbow extensor
 Triceps brachii
 Anconeus provides assistance
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Muscles
 Radioulnar pronators
 Pronator teres
 Pronator quadratus
 Brachioradialis
 Radioulnar supinators
 Biceps brachii
 Supinator muscle
 Brachioradialis

26. Tennis Elbow
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Lateral epicondylitis
Tennis elbow common problem usually
involving extensor digitorum muscle near its
origin on lateral epicondyle
 known lateral epicondylitis
 associated with gripping & lifting activities

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33. Golfer’s Elbow
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 Medial epicondylitis
 somewhat less common
 known as golfer's elbow
 associated with medial wrist flexor & pronator group
near their origin on medial epicondyle
 Both conditions involve muscles which cross elbow
but act primarily on wrist & hand

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Muscles
 Anterior
 Primarily flexion &
pronation
 Biceps brachii
 Brachialis
 Brachioradialis
 Pronator teres
 Pronator quadratus

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Muscles
 Posterior
 Primarily extension &
supination
 Triceps brachii
 Anconeus
 Supinator

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Nerves
 All elbow & radioulnar joints muscles are innervated
from median, musculotaneous, & radial nerves of
brachial plexus

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Nerves
 Median nerve - derived from C6 &
C7
 Pronator teres
 Pronator quadratus (anterior
interosseus nerve)
 Sensation to palmar aspect of hand
& first three phalanges, palmar
aspect of radial side of fourth finger,
dorsal aspect of index & long fingers

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Nerves
 Musculotaneous nerve -
branches from C5 & C6
 Biceps brachii
 Brachialis

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Biceps Brachii Muscle
Flexion of elbow
Supination of
forearm
Weak flexion of
shoulder joint
Weak abduction of
shoulder joint when
externally rotated

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Brachialis Muscle
True
flexion of
elbow

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Brachioradialis Muscle
Flexion of elbow
Pronation from supinated
position to neutral
Supination from pronated
position to neutral

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Triceps Brachii Muscle
Long head:
extension of
shoulder joint;
adduction of
shoulder joint;
horizontal
abduction
All heads:
extension of
elbow

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Anconeus Muscle
Extension of elbow

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Pronator Teres Muscle
Pronation of
forearm
Weak flexion of
elbow

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Pronator Quadratus Muscle
Pronation of
forearm

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Supinator Muscle
Supination of
forearm

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Elbow Flexion
 Ex. Biceps curl
 Agonists
 Biceps brachii
 Brachialis
 Brachioradialis

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Elbow Extension
 EX. Push-up
 Agonists
 Triceps brachii
 Anconeus

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Radioulnar Pronation
 Agonists
 Pronator teres
 Pronator quadratus
 Brachioradialis

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Radioulnar Supination
 Ex. Tightening a screw
 Agonists
 Biceps brachii
 Supinator muscle
 Brachioradialis