Lecture 8
Biomechanics of the Elbow
Joints of the Elbow
 Humeroulnar
 Humeroradial
 Radioulnar – superior/inferior
Composite trochoginglymoid joint – trochoid or pivot and ginglymoid or
hinge (diarthrodial uniaxial)
Permits two degrees of freedom
 Flexion/extension – humeroulnar/humeroradial
 Pronation/supination – radioulnar superior/inferior
Humeroradial and humeroulnar joints
Stability
 Bony stability via the ulna/trochlea fossa and humerus/trochlea
 Coronoid process provides  resistance to posterior dislocation
as elbow flexes
 Humeroradial joint provides resistance vs. valgus stresses &
prevents posterior dislocation beyond 90 degrees
 Ligaments of the Elbow
1. Collateral ligaments
A. Medial (triangular) –
1) Anterior fibers – primary stabilizer vs. valgus stress
(20-120 deg)
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2) oblique fibers – vs. valgus stress and assitsts in
approximation
3) posterior- vs. valgus stress
B. Lateral (fan) –
 weaker of the 2 collaterals – attaches to annular
ligament
 stabilizer vs. varus stress - poor vs. tensile forces
 Anconeus assists in stability vs. varus forces
2. Joint capsule that encompasses humeroulna, humeroradial,
and proximal radioulna joints
Carrying angle
 Formed by the intersection of the long axis of the humerus and
long axis of ulna with elbow extended and supinated (anatomical
position)
 Normal – 10-15 degrees of valgus (> in )
 Trochlea extends further distally than capitulum (this also occurs
within the trochlea itself)
> carrying angle  > valgus stress on elbow  > tensile forces medially 
> compressive forces medially
Range of Motion
 Flexion/extension – 0 – 140 degrees
 Gliding motion with final 5-10 degrees rolling
 Functional ROM – (20 [rising from chair] – 136 [talking on
phone] degrees)
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Musculature
Flexors
Brachialis (humerus  coronoid process)
Biceps (coracoid process/supraglenoid tubercle  radial tuberosity)
Brachioradialis (lateral humerus  distal radius)
Role dependent on:
1. Location of muscles
2. Position of elbow and adjacent joints (active and passive
insufficiency)
3. Position of forearm
4. Magnitude of applied load
5. Type of contraction
6. Speed of motion
Brachialis
 Spurt or mobility muscle (insertion is close to joint axis)– greatest
force production (100 deg)  greatest MA
 Position of forearm does not change function
 Functions throughout ROM; regardless of load, type of
contraction, or speed of contraction
Biceps Brachii
 Spurt or mobility muscle – torque greatest between 80-100 degrees
 Provides mainly a translatory/compressive force in extension –
becomes distractive beyond 100 deg flexion
 Inactive during unresisted flexion with forearm pronated, but
active with resisted flexion regardless of forearm position
 actively insufficient with elbow and shoulder flexion and
supination
Brachioradialis
 shunt muscle – distal insertion
 provides mainly compressive force
 affected by speed of activity -  speed   activity
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Extensors
Triceps
 long head affected by shoulder position  A.I. with full shoulder
extension
 greatest torque generated with elbow at 90 degrees depending on
the position of the shoulder
Anconeus
 assists in elbow extension – stabilizer during pronation/supination
Radioulnar Joints (Superior/Inferior)
Stability – predominantly ligamentous
 Ligaments
1. Annular – prevents dislocation of radial head – lined with
articular cartilage
2. Quadrate – (inferior edge of radial notch of ulna neck of
radius)
 Reinforces inferior aspect of capsule
 Helps radial head maintain position
 Limits rotation of radial head
3. Oblique Cord (just inferior to radial notch of ulnabiceps
tuberosity
4. Interosseous Membrane
 Binds radius and ulna together
 Provides for transmission of forces between the 2 bones
 Under tension in neutral – relaxed in
supination/pronation
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5. Anterior and inferior radioulnar ligaments (distal)
Axis of Rotation
 Through capitulum  radial head  upper ½ of radial shaft 
ulna styloid process
ROM
 Pronation/supination – 70/85 (AAOS), 80/80 (AMA), 80-90 both
pronation/supination
 Functional ROM – 49 deg pronation (reading newspaper) –
52 deg supination (fork to mouth)
Musculature
Pronator teres – (medial epicondyle to radius)
 Pronates
 Stabilizes superior radioulnar jt
 Maintain position of radial head in capitulum
Pronator quadratus (anterior surface of ulna  anterior surface of radius)
 Pronates
 Stabilizes distal radioulnar jt.
Biceps Brachii
 Active during resisted supination and fast supination with elbow at
90 deg
Supinator (lateral epicondyle  lateral/anterior radius
 Alone produces unresisted, slow supination in any elbow position
Muscles that control the hand and wrist cross the elbow joint, therefore the
position of the elbow affects muscle function in the hand, and the hand/wrist
muscles affect the elbow.
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Wrist/finger flexor muscles originate from medial epicondyle of humerus,
extensor muscles from the lateral epicondyle.
These muscles reinforce the elbow joint capsule providing stability to the
elbow complex.
Produce compressive forces at the elbow and can contribute to torque
production.
Injuries
Compressive forces transmitted to elbow – extended (close-pack position)
 Radial head fx
 Coronoid or olecranon fx
 Supracondyler region of humerus
Children susceptible to dislocation of radial head from annular ligament
(nursemaid’s elbow) secondary to excessive tensile forces.
Medial collateral ligament is susceptible to tensile stresses during the
cocking phase of throwing.
Multiple repetitions  medial collateral ligamentous laxity  increased
compressive forces laterally on capitulum interruption of vascular supply
 avascular necroses of radial head or epiphyseal plate fx in children
Tennis Elbow – lateral epicondylitis
Repeated forceful contraction of ECRB at its origin (excessive and repeated
tensile forces)  microtears in tendon  inflammation
Golfer’s Elbow – medial epicondylitis
Repeated forceful contractions of pronator teres, FCR, and/or occasionally
FCU
Cubital tunnel syndrome
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Compression of ulnar n. by FCU as it traverses the medial epicondyle and
olecranon process  impaired motion of 4th and 5th digits and thumb
(adductor pollicis and flexor pollicis brevis)
Supracondylar fx  injure radial (extensor deficits) and/or median (flexors,
pronators, lumbricales) nerves or brachial artery
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