Transcript Anatomy & Biomechanics of the Shoulder James J. Irrgang, Ph.D., PT, ATC

Anatomy & Biomechanics
of the Shoulder
James J. Irrgang, Ph.D., PT, ATC
Department of Physical Therapy
University of Pittsburgh
Shoulder Motion
Combined Movements:
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Flexion - 150 - 1800
Extension - 50 - 600
Abduction - 150 - 1800
External rotation - 900
Internal rotation - 70 - 900
Horizontal abduction
Horizontal adduction
Shoulder Girdle
Includes:
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G-H joint
A-C joint
S-C joint
S-T joint
Subacromial space
Glenohumeral Motion
Controlled by:
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Passive restraints
Active restraints
Glenohumeral Motion
Passive Restraints:
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Bony geometry
Labrum
Capsuloligamen
tous structures
Negative intraarticular
pressure
Capsuloligamentous Structures
Glenohumeral ligaments:
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SGHL
MGHL
IGHL complex
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anterior band
posterior band
axillary pouch
Capsuloligamentous Structures
Glenohumeral ligaments:
Capsuloligamentous
Structures
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Coracohumeral ligament
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anterior band
posterior band
Restraints to External
Rotation
Dependent on arm position:
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00 - SGHL, C-H &
subscapularis
450 - SGHL & MGHL
900 - anterior band
IGHLC
Restraints to Internal Rotation
Dependent on arm position:
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00 - posterior band
IGHLC
450 - anterior &
posterior band IGHLC
900 - anterior &
posterior band IGHLC
Restraints to Inferior
Translation
Dependent on arm position:
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00 - SGHL & C-H
900 - IGHLC
Glenohumeral Motion
Scapular Plane:
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Flexion/extension - 1200
Abduction/adduction - 1200
External/internal rotation
Horizontal abduction/
adduction
Arthrokinematics of
Glenohumeral Joint
Glenohumeral Motion
Convex - Concave Rule:
Glenohumeral Motion
Arthrokinematics:
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Abduction
Flexion
Extension
External rotation
Internal rotation
Glenohumeral Motion
Arthrokinematics:
Harryman et. al. 1990
Glenohumeral Motion
Arthrokinematics:
Harryman et. al. 1990
Glenohumeral Motion
Arthrokinematics:
Harryman et. al. 1990
Glenohumeral Motion
Capsular Tightness:
Results in Abnormal
Arthrokinematics
Glenohumeral Motion
Normal Arthrokinematics:
•Combines
rotation &
translation to keep humeral
head centered on glenoid
Scapulohumeral Muscles
Prime Movers:
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Deltoid
Pectoralis major
Latissimus dorsi
Teres major
Biceps
Coracobrachialis
Triceps
Scapulohumeral Muscles
Rotator Cuff:
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Subscapularis
Supraspinatus
Infraspinatus
Teres Minor
Rotator Cuff Function
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Approximates
humerus to function
Supraspinatus
assists deltoid in
abduction
Subscapularis,
infraspinatus &
teres minor depress
humeral head
Subscapularis
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Effective restraint to
ER with arm at side
Ineffective restraint
to ER with arm
abducted to 900
Turkel et. al. JBJS 1981
Infraspinatus/Teres Minor
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Reduces strain on
anterior band of
IGHLC
“Hamstrings” of
glenohumeral joint
Cain et. al. AJSM 1987
Long Head of Biceps
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Biceps tendon force
increases torsional
rigidity to ER
No effect on strain of
IGHLC
Effect lost with SLAP
lesion
Rodosky et. al. AJSM 1994
Biceps Becomes More Important
Anterior Stabilizer as
Capsuloligamentous Stability
Decreases
Itoi et. al. JBJS 1994 &
Glousman et. al. 1988
Force Couples Acting on
Glenohumeral Joint
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Transverse plane anterior vs. posterior
RC
Coronal plane deltoid vs. inferior
RC
Rotator Cuff Tear
Supraspinatus:
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Essential force
couples maintained
Normal strength &
function possible
Rotator Cuff Tear
Supraspinatus/Posterior Cuff:
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Essential force
couples disrupted
Weakness with
external rotation
Little active elevation
possible
Rotator Cuff Tear
Massive Tear :
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Essential force
couples disrupted
Weakness with
internal & external
rotation
Little active elevation
possible
Subacromial Space
Structures Within Suprahumeral Space
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Long head of biceps
Superior capsule
Supraspinatus tendon
Upper margins of
subscapularis &
infraspinatus tendons
Subacromial bursa
Inferior surface of A-C
joint
Subacromial Space
Clinical Relevance:
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Avoidance of impingement during
elevation of arm requires:
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external rotation of humerus to clear
greater tuberosity
upward rotation of scapula to elevate
lateral end of acromion
Subacromial Space
Clinical Relevance:
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Primary impingement:
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structural stenosis of subacromial space
Secondary impingement:
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functional stenosis of subacromial space
due to abnormal arthrokinematics
Scapulothoracic Joint
Scapulothoracic Muscles
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Trapezius
Serratus anterior
Rhomboids
Levator scapulae
Pectoralis minor
Subclavius
Scapulothoracic Motion
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Elevation/depression
Protraction/retraction
Upward/downward
rotation
Force Couple at
Scapulothoracic Joint
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Serratus anterior produces
anterio-lateral movement of
inferior angle
Upper trapezius pulls
scapula medially
Scapulohumeral Rhythm
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Total elevation:
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1200 at G-H joint
600 at S-T joint
Force Couple at
Scapulothoracic Joint
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Serratus anterior produces
anterio-lateral movement of
inferior angle
Upper trapezius pulls
scapula medially
Acromioclavicular Joint
Acromioclavicular Joint
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Joint capsule
A-C ligaments
Intra-articular disc
Coracoclavicular
ligaments
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conoid (medial)
trapezoid (lateral)
Acromioclavicular Joint
Movements:
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Axial rotation of clavicle
(spin)
Angulation between scapula
& clavicle
Sternoclavicular Joint
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Joint capsule
Anterior & posterior SC ligaments
Intra-articular disc
Interclavicular
ligament
Costoclavicular
ligament
Sternoclavicular Joint
Motions:
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Protraction/retraction
Elevation/depression
Axial rotation (spin)
Biomechanics of
Scapular Rotation
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Scapulothoracic motion
occurs as part of closed
kinetic chain involving:
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A-C joint
S-C joint
Scapular Rotation
Phase I
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Upper & lower portions of
trapezius & serratus
anterior produce upward
rotatory force on scapula
Motion at A-C joint
prevented by
coracoclavicular ligament
Rotation of scapula
occurs as elevation of
clavicle at S-C joint
Scapular Rotation
Phase II
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Further motion at S-C
joint prevented by
costoclavicular ligament
Continued upward
rotation of scapula pulls
on costoclavicular
ligament causing
posterior rotation of
clavicle
Posterior rotation of
clavicle allows further
upward rotation of
scapula
Scapular Rotation
Necessary to:
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Enhance glenohumeral
stability
Elevate acromion to avoid
impingement
Maintain effective length
tension relationship of
scapulohumeral muscles
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