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:
Glenohumeral MotionGlenohumeral Motion
• 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
Dependent on arm position:
Restraints to Inferior Restraints to Inferior TranslationTranslation
• 00 - SGHL & C-H• 900 - IGHLC
Dependent on arm position:
Glenohumeral MotionGlenohumeral Motion
• Flexion/extension - 1200
• Abduction/adduction - 1200
• External/internal rotation• Horizontal abduction/
adduction
Scapular Plane:
Arthrokinematics of Glenohumeral Joint
Glenohumeral MotionGlenohumeral Motion
Convex - Concave Rule:
Glenohumeral MotionGlenohumeral Motion
• Abduction• Flexion• Extension• External rotation• Internal rotation
Arthrokinematics:
Glenohumeral MotionGlenohumeral Motion
Arthrokinematics:
Harryman et. al. 1990
Glenohumeral MotionGlenohumeral Motion
Arthrokinematics:
Harryman et. al. 1990
Glenohumeral MotionGlenohumeral Motion
Arthrokinematics:
Harryman et. al. 1990
Glenohumeral MotionGlenohumeral Motion
Results in Abnormal Arthrokinematics
Capsular Tightness:
Glenohumeral MotionGlenohumeral Motion
•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:
Rotator Cuff TearRotator Cuff Tear
• Essential force couples disrupted
• Weakness with external rotation
• Little active elevation possible
Supraspinatus/Posterior Cuff:
Rotator Cuff TearRotator Cuff Tear
• 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
Subacromial SpaceSubacromial Space
• 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:
Subacromial SpaceSubacromial Space
• 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
Acromioclavicular JointAcromioclavicular Joint
• Joint capsule• A-C ligaments• Intra-articular disc• Coracoclavicular
ligaments• conoid (medial)• trapezoid (lateral)
Acromioclavicular JointAcromioclavicular Joint
• 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
Scapular RotationScapular Rotation
• 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
Scapular RotationScapular Rotation
• Enhance glenohumeral stability
• Elevate acromion to avoid impingement
• Maintain effective length tension relationship of scapulohumeral muscles
Necessary to:
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