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

Anatomy & Biomechanics Anatomy & Biomechanics of the Shoulderof the Shoulder

James J. Irrgang, Ph.D., PT, ATCDepartment of Physical Therapy

University of Pittsburgh

Shoulder MotionShoulder Motion

• Flexion - 150 - 1800

• Extension - 50 - 600

• Abduction - 150 - 1800

• External rotation - 900

• Internal rotation - 70 - 900

• Horizontal abduction• Horizontal adduction

Combined Movements:

Shoulder GirdleShoulder Girdle

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

Includes:

Glenohumeral MotionGlenohumeral Motion

• Passive restraints• Active restraints

Controlled by:


• Bony geometry• Labrum• Capsuloligamen

tous structures• Negative intra-

articular pressure

Passive Restraints:

Capsuloligamentous StructuresCapsuloligamentous Structures

• SGHL• MGHL• IGHL complex

• anterior band• posterior band• axillary pouch

Glenohumeral ligaments:

Capsuloligamentous StructuresCapsuloligamentous Structures

Glenohumeral ligaments:

Capsuloligamentous Capsuloligamentous StructuresStructures

• Coracohumeral ligament• anterior band• posterior band

Restraints to External Restraints to External RotationRotation

• 00 - SGHL, C-H & subscapularis

• 450 - SGHL & MGHL• 900 - anterior band

IGHLC

Dependent on arm position:

Restraints to Internal RotationRestraints to Internal Rotation

• 00 - posterior band IGHLC

• 450 - anterior & posterior band IGHLC

• 900 - anterior & posterior band IGHLC


Restraints to Inferior Restraints to Inferior TranslationTranslation

• 00 - SGHL & C-H• 900 - IGHLC



• Flexion/extension - 1200

• Abduction/adduction - 1200

• External/internal rotation• Horizontal abduction/

adduction

Scapular Plane:

Arthrokinematics of Glenohumeral Joint


Convex - Concave Rule:


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

Arthrokinematics:


Arthrokinematics:

Harryman et. al. 1990


Results in Abnormal Arthrokinematics

Capsular Tightness:


•Combines rotation & translation to keep humeral head centered on glenoid

Normal Arthrokinematics:

Scapulohumeral MusclesScapulohumeral Muscles

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

Prime Movers:

Scapulohumeral MusclesScapulohumeral Muscles

• Subscapularis• Supraspinatus• Infraspinatus• Teres Minor

Rotator Cuff:

Rotator Cuff FunctionRotator Cuff Function

• Approximates humerus to function

• Supraspinatus assists deltoid in abduction

• Subscapularis, infraspinatus & teres minor depress humeral head

SubscapularisSubscapularis

• Effective restraint to ER with arm at side

• Ineffective restraint to ER with arm abducted to 900

Turkel et. al. JBJS 1981

Infraspinatus/Teres MinorInfraspinatus/Teres Minor

• Reduces strain on anterior band of IGHLC

• “Hamstrings” of glenohumeral joint

Cain et. al. AJSM 1987

Long Head of BicepsLong 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

Biceps Becomes More Important Anterior Stabilizer as Capsuloligamentous Stability Decreases

Itoi et. al. JBJS 1994 &Glousman et. al. 1988

Force Couples Acting on Force Couples Acting on Glenohumeral JointGlenohumeral Joint

• Transverse plane - anterior vs. posterior RC

• Coronal plane - deltoid vs. inferior RC

Rotator Cuff TearRotator Cuff Tear

• Essential force couples maintained

• Normal strength & function possible

Supraspinatus:


• Essential force couples disrupted

• Weakness with external rotation

• Little active elevation possible

Supraspinatus/Posterior Cuff:


• Essential force couples disrupted

• Weakness with internal & external rotation

• Little active elevation possible

Massive Tear :

Subacromial SpaceSubacromial Space

Structures Within Suprahumeral SpaceStructures 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


• 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

Clinical Relevance:


• Primary impingement:• structural stenosis of subacromial space

• Secondary impingement:• functional stenosis of subacromial space

due to abnormal arthrokinematics

Clinical Relevance:

Scapulothoracic JointScapulothoracic Joint

Scapulothoracic MusclesScapulothoracic Muscles

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

Scapulothoracic MotionScapulothoracic Motion

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

rotation

Force Couple atForce Couple atScapulothoracic JointScapulothoracic Joint

• Serratus anterior produces anterio-lateral movement of inferior angle

• Upper trapezius pulls scapula medially

Scapulohumeral RhythmScapulohumeral Rhythm

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

Force Couple atForce Couple atScapulothoracic JointScapulothoracic Joint

• Serratus anterior produces anterio-lateral movement of inferior angle

• Upper trapezius pulls scapula medially

Acromioclavicular JointAcromioclavicular Joint


• Joint capsule• A-C ligaments• Intra-articular disc• Coracoclavicular

ligaments• conoid (medial)• trapezoid (lateral)


• Axial rotation of clavicle (spin)

• Angulation between scapula & clavicle

Movements:

Sternoclavicular JointSternoclavicular Joint

• Joint capsule• Anterior & posterior S-

C ligaments• Intra-articular disc• Interclavicular

ligament• Costoclavicular

ligament

Sternoclavicular JointSternoclavicular Joint

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

Motions:

Biomechanics of Biomechanics of Scapular RotationScapular Rotation

• Scapulothoracic motion occurs as part of closed kinetic chain involving:

• A-C joint• S-C joint

Scapular RotationScapular Rotation

• 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

Phase I


• 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

Phase II


• Enhance glenohumeral stability

• Elevate acromion to avoid impingement

• Maintain effective length tension relationship of scapulohumeral muscles

Necessary to:

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