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Anatomy & Biomechanics of the Shoulder. James J. Irrgang, Ph.D., PT, ATC Department of Physical Therapy University of Pittsburgh. Shoulder Motion. Combined Movements:. Flexion - 150 - 180 0 Extension - 50 - 60 0 Abduction - 150 - 180 0 External rotation - 90 0

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anatomy biomechanics of the shoulder
Anatomy & Biomechanics of the Shoulder

James J. Irrgang, Ph.D., PT, ATC

Department of Physical Therapy

University of Pittsburgh

shoulder motion
Shoulder Motion

Combined Movements:

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

Includes:

  • G-H joint
  • A-C joint
  • S-C joint
  • S-T joint
  • Subacromial space
glenohumeral motion
Glenohumeral Motion

Controlled by:

  • Passive restraints
  • Active restraints
glenohumeral motion5
Glenohumeral Motion

Passive Restraints:

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

Glenohumeral ligaments:

  • SGHL
  • MGHL
  • IGHL complex
    • anterior band
    • posterior band
    • axillary pouch
capsuloligamentous structures7
Capsuloligamentous Structures

Glenohumeral ligaments:

capsuloligamentous structures8
Capsuloligamentous Structures
  • Coracohumeral ligament
    • anterior band
    • posterior band
restraints to external rotation
Restraints to External Rotation

Dependent on arm position:

  • 00 - SGHL, C-H & subscapularis
  • 450 - SGHL & MGHL
  • 900 - anterior band IGHLC
restraints to internal rotation
Restraints to Internal Rotation

Dependent on arm position:

  • 00 - posterior band IGHLC
  • 450 - anterior & posterior band IGHLC
  • 900 - anterior & posterior band IGHLC
restraints to inferior translation
Restraints to Inferior Translation

Dependent on arm position:

  • 00 - SGHL & C-H
  • 900 - IGHLC
glenohumeral motion12
Glenohumeral Motion

Scapular Plane:

  • Flexion/extension - 1200
  • Abduction/adduction - 1200
  • External/internal rotation
  • Horizontal abduction/ adduction
glenohumeral motion14
Glenohumeral Motion

Convex - Concave Rule:

glenohumeral motion15
Glenohumeral Motion

Arthrokinematics:

  • Abduction
  • Flexion
  • Extension
  • External rotation
  • Internal rotation
glenohumeral motion16
Glenohumeral Motion

Arthrokinematics:

Harryman et. al. 1990

glenohumeral motion17
Glenohumeral Motion

Arthrokinematics:

Harryman et. al. 1990

glenohumeral motion18
Glenohumeral Motion

Arthrokinematics:

Harryman et. al. 1990

glenohumeral motion19

Glenohumeral Motion

Capsular Tightness:

Results in Abnormal Arthrokinematics

glenohumeral motion20

Glenohumeral Motion

Normal Arthrokinematics:

Combines rotation & translation to keep humeral head centered on glenoid

scapulohumeral muscles
Deltoid

Pectoralis major

Latissimus dorsi

Teres major

Biceps

Coracobrachialis

Triceps

Scapulohumeral Muscles

Prime Movers:

scapulohumeral muscles22
Scapulohumeral Muscles

Rotator Cuff:

  • Subscapularis
  • Supraspinatus
  • Infraspinatus
  • Teres Minor
rotator cuff function
Rotator Cuff Function
  • Approximates humerus to function
  • Supraspinatus assists deltoid in abduction
  • Subscapularis, infraspinatus & teres minor depress humeral head
subscapularis
Subscapularis
  • 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
Infraspinatus/Teres Minor
  • Reduces strain on anterior band of IGHLC
  • “Hamstrings” of glenohumeral joint

Cain et. al. AJSM 1987

long head of biceps
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

slide27
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
Force Couples Acting on Glenohumeral Joint
  • Transverse plane - anterior vs. posterior RC
  • Coronal plane - deltoid vs. inferior RC
rotator cuff tear
Rotator Cuff Tear

Supraspinatus:

  • Essential force couples maintained
  • Normal strength & function possible
rotator cuff tear30
Rotator Cuff Tear

Supraspinatus/Posterior Cuff:

  • Essential force couples disrupted
  • Weakness with external rotation
  • Little active elevation possible
rotator cuff tear31
Rotator Cuff Tear

Massive Tear :

  • Essential force couples disrupted
  • Weakness with internal & external rotation
  • Little active elevation possible
structures within suprahumeral space
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
subacromial space34
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
subacromial space35
Subacromial Space

Clinical Relevance:

  • Primary impingement:
    • structural stenosis of subacromial space
  • Secondary impingement:
    • functional stenosis of subacromial space due to abnormal arthrokinematics
scapulothoracic muscles
Scapulothoracic Muscles
  • Trapezius
  • Serratus anterior
  • Rhomboids
  • Levator scapulae
  • Pectoralis minor
  • Subclavius
scapulothoracic motion
Scapulothoracic Motion
  • Elevation/depression
  • Protraction/retraction
  • Upward/downward rotation
force couple at scapulothoracic joint
Force Couple atScapulothoracic Joint
  • Serratus anterior produces anterio-lateral movement of inferior angle
  • Upper trapezius pulls scapula medially
scapulohumeral rhythm
Scapulohumeral Rhythm
  • Total elevation:
    • 1200 at G-H joint
    • 600 at S-T joint
force couple at scapulothoracic joint41
Force Couple atScapulothoracic Joint
  • Serratus anterior produces anterio-lateral movement of inferior angle
  • Upper trapezius pulls scapula medially
acromioclavicular joint43
Acromioclavicular Joint
  • Joint capsule
  • A-C ligaments
  • Intra-articular disc
  • Coracoclavicular ligaments
    • conoid (medial)
    • trapezoid (lateral)
acromioclavicular joint44
Acromioclavicular Joint

Movements:

  • Axial rotation of clavicle (spin)
  • Angulation between scapula & clavicle
sternoclavicular joint
Sternoclavicular Joint
  • Joint capsule
  • Anterior & posterior S-C ligaments
  • Intra-articular disc
  • Interclavicular ligament
  • Costoclavicular ligament
sternoclavicular joint46
Sternoclavicular Joint

Motions:

  • Protraction/retraction
  • Elevation/depression
  • Axial rotation (spin)
biomechanics of scapular rotation
Biomechanics of Scapular Rotation
  • Scapulothoracic motion occurs as part of closed kinetic chain involving:
        • A-C joint
        • S-C joint
scapular rotation
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
scapular rotation49
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
scapular rotation50
Scapular Rotation

Necessary to:

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

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