Anatomy

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Anatomy Biomechanics of the Shoulder

• James J. Irrgang, Ph.D., PT, ATC
• Department of Physical Therapy
• University of Pittsburgh

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Shoulder Motion
Combined Movements

• Flexion - 150 - 1800
• Extension - 50 - 600
• Abduction - 150 - 1800
• External rotation - 900
• Internal rotation - 70 - 900
• Horizontal abduction
• Horizontal adduction

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Shoulder Girdle
Includes

• G-H joint
• A-C joint
• S-C joint
• S-T joint
• Subacromial space

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Glenohumeral Motion
Controlled by

• Passive restraints
• Active restraints

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Glenohumeral Motion
Passive Restraints

• Bony geometry
• Labrum
• Capsuloligamentous structures
• Negative intra-articular pressure

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Capsuloligamentous Structures
Glenohumeral ligaments

• SGHL
• MGHL
• IGHL complex
• anterior band
• posterior band
• axillary pouch

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Capsuloligamentous Structures
Glenohumeral ligaments
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Capsuloligamentous Structures

• Coracohumeral ligament
• anterior band
• posterior band

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Restraints to External Rotation
Dependent on arm position

• 00 - SGHL, C-H subscapularis
• 450 - SGHL MGHL
• 900 - anterior band IGHLC

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Restraints to Internal Rotation
Dependent on arm position

• 00 - posterior band IGHLC
• 450 - anterior posterior band IGHLC
• 900 - anterior posterior band IGHLC

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Restraints to Inferior Translation
Dependent on arm position

• 00 - SGHL C-H
• 900 - IGHLC

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Glenohumeral Motion
Scapular Plane

• Flexion/extension - 1200
• Abduction/adduction - 1200
• External/internal rotation
• Horizontal abduction/ adduction

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• Arthrokinematics of Glenohumeral Joint

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Glenohumeral Motion
Convex - Concave Rule
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Glenohumeral Motion
Arthrokinematics

• Abduction
• Flexion
• Extension
• External rotation
• Internal rotation

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Glenohumeral Motion
Arthrokinematics
Harryman et. al. 1990
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Glenohumeral Motion
Arthrokinematics
Harryman et. al. 1990
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Glenohumeral Motion
Arthrokinematics
Harryman et. al. 1990
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Glenohumeral Motion
Capsular Tightness

• Results in Abnormal Arthrokinematics

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Glenohumeral Motion
Normal Arthrokinematics

• Combines rotation translation to keep humeral
  head centered on glenoid

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Scapulohumeral Muscles
Prime Movers

• Deltoid
• Pectoralis major
• Latissimus dorsi
• Teres major
• Biceps
• Coracobrachialis
• Triceps

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Scapulohumeral Muscles
Rotator Cuff

• Subscapularis
• Supraspinatus
• Infraspinatus
• Teres Minor

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Rotator Cuff Function

• Approximates humerus to function
• Supraspinatus assists deltoid in abduction
• Subscapularis, infraspinatus teres minor
  depress humeral head

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Subscapularis

• Effective restraint to ER with arm at side
• Ineffective restraint to ER with arm abducted to
  900

Turkel et. al. JBJS 1981
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Infraspinatus/Teres Minor

• Reduces strain on anterior band of IGHLC
• Hamstrings of glenohumeral joint

Cain et. al. AJSM 1987
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Long Head of Biceps

• Biceps tendon force increases torsional rigidity
  to ER
• No effect on strain of IGHLC
• Effect lost with SLAP lesion

Rodosky et. al. AJSM 1994
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• Biceps Becomes More Important Anterior
  Stabilizer as Capsuloligamentous Stability
  Decreases

Itoi et. al. JBJS 1994 Glousman et. al. 1988
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Force Couples Acting on Glenohumeral Joint

• Transverse plane - anterior vs. posterior RC
• Coronal plane - deltoid vs. inferior RC

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Rotator Cuff Tear
Supraspinatus

• Essential force couples maintained
• Normal strength function possible

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Rotator Cuff Tear
Supraspinatus/Posterior Cuff

• Essential force couples disrupted
• Weakness with external rotation
• Little active elevation possible

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Rotator Cuff Tear
Massive Tear

• Essential force couples disrupted
• Weakness with internal external rotation
• Little active elevation possible

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Subacromial Space
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Structures Within Suprahumeral Space

• Long head of biceps
• Superior capsule
• Supraspinatus tendon
• Upper margins of subscapularis infraspinatus
  tendons
• Subacromial bursa
• Inferior surface of A-C joint

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Subacromial Space
Clinical Relevance

• Avoidance of impingement during elevation of arm
  requires
• external rotation of humerus to clear greater
  tuberosity
• upward rotation of scapula to elevate lateral end
  of acromion

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Subacromial Space
Clinical Relevance

• Primary impingement
• structural stenosis of subacromial space
• Secondary impingement
• functional stenosis of subacromial space due to
  abnormal arthrokinematics

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Scapulothoracic Joint
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Scapulothoracic Muscles

• Trapezius
• Serratus anterior
• Rhomboids
• Levator scapulae
• Pectoralis minor
• Subclavius

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Scapulothoracic Motion

• Elevation/depression
• Protraction/retraction
• Upward/downward rotation

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Force Couple atScapulothoracic Joint

• Serratus anterior produces anterio-lateral
  movement of inferior angle
• Upper trapezius pulls scapula medially

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Scapulohumeral Rhythm

• Total elevation
• 1200 at G-H joint
• 600 at S-T joint

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Force Couple atScapulothoracic Joint

• Serratus anterior produces anterio-lateral
  movement of inferior angle
• Upper trapezius pulls scapula medially

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Acromioclavicular Joint
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Acromioclavicular Joint

• Joint capsule
• A-C ligaments
• Intra-articular disc
• Coracoclavicular ligaments
• conoid (medial)
• trapezoid (lateral)

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Acromioclavicular Joint
Movements

• Axial rotation of clavicle (spin)
• Angulation between scapula clavicle

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Sternoclavicular Joint

• Joint capsule
• Anterior posterior S-C ligaments
• Intra-articular disc
• Interclavicular ligament
• Costoclavicular ligament

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Sternoclavicular Joint
Motions

• Protraction/retraction
• Elevation/depression
• Axial rotation (spin)

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Biomechanics of Scapular Rotation

• Scapulothoracic motion occurs as part of closed
  kinetic chain involving
• A-C joint
• S-C joint

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Scapular Rotation
Phase I

• 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

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Scapular Rotation
Phase II

• 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

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Scapular Rotation
Necessary to

• Enhance glenohumeral stability
• Elevate acromion to avoid impingement
• Maintain effective length tension relationship of
  scapulohumeral muscles

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