Kinesiology, NTUPT

The Shoulder Complex

Functions of the Shoulder Complex
Structure of the Shoulder Complex
Kinematics of the Shoulder Complex
Muscles at the Shoulder
Shoulder Stability
Mechanism of Injury at the Shoulder

Objectives： After studying this topic, the students will be able to

to identify the structure of the shoulder and the shoulder girdle, including joint type, articular shape, and the surrounding tissues
to describe joint motions occurring at the shoulder complex, including osteokinematic and arthrokinematic movements, muscle actions, and factors checking shoulder motions
to understand the stability mechanism of the shoulder complex and the possible mechanisms of injury
to distinguish the three-degree-of-freedom joint from the one- or two-degree-of-freedom joint
to understand the effect of muscle synergies and the influence of weakness or paralysis of one single muscle in coupled-muscle motions

Neumann DA (2002). Shoulder complex. In Neumann DA: Kinesiology of the Musculoskeletal System: Foundations for Physical Rehabilitation. Philadelphia: Mosby. Chapter 5, pp. 91-132
Smith LK, Weiss EL, Don Lehmkuhl L (eds, 1996). Brunnstrom's Clinical Kinesiology, 5th ed. Philadelphia, F.A. Davis. Chapter 5, pp. 223-225
Craig J et al. (2001). Biomechanics of the shoulder. In Nordin M & Frankel VH: Basic Biomechanics of the Musculoskeletal System. Philadelphia: Lippincott Williams & Wilkins. Chapter 12, pp.318-339

Functions of the Shoulder Complex

To link the upper extremity to the trunk

dependent arm position

control of rotator cuff muscles

To provide extensive mobility of the arm in space

To provide stability for elbow and hand skillful or forceful movements

Joint Structure of the Shoulder Complex

Joints at the shoulder complex

glenohumeral joint (shoulder joint) sternoclavicular joint acromioclavicular joint scapulothoracic articulation： msucle-bone articulation NOTE： classified by Smith et al., 1996 bony articulations gelnohumeral joint sternoclavicular joint acromioclavicular joint
functional joints scapulothoracic articulation suprahumeral articulation (subacromial articulation)： the articulation between the coracoacromial ligament and the humerus bicipital groove： the groove between the greater and lesser tuberosities of the humerus

Glenohumeral joint (GH joint)

proximal component： scapula

concave glenoid cavity covered with glenoid labrum that is a fibrocartilage to deepen the glenoid cavity

distal component： humerus

convex humeral head

retroversion of the humeral head about 30º posterior to the frontal axis of the elbow joint

joint type： ball-and-socket joint

motion： convex on concave

shoulder flexion/ extension with posterior/ anterior glide of the humeral head on the glenooid cavity

shoulder abduction/ adduction with inferior/ superior glide of the humeral head on the glenooid cavity

shoulder internal/ external rotation with posterior/ anterior glide of the humeral head on the glenooid cavity

shoulder horizontal abduction/ horizontal adduction with anterior/ posterior glide of the humeral head on the glenooid cavity

DOF = 3

neutral position： anatomic position

resting position： 70° of shoulder abduction and 30° of flexion (horizontal adduction)

closed packed position： 90° of shoulder abduction and full external rotation

Joints at shoulder complex

Sternoclavicular joint (SC joint)

proximal component： sternum saddle-shaped sternal manubrium distal component： clavicle saddle-shaped medial end of the clavicle disc between 2 articular surfaces joint type： saddle joint motion： shoulder girdle motion clavicle elevation/ depression clavicle protraction/ depression clavicle posterior rotation DOF = 3

NOTE： clavicle convex forward medially and concave forward laterally quadripedal animals do not have clavicles isokinetic strength of shoulder flexor and abductor decreases 50% if the clavicle is removed

Joints at shoulder complex

Acromioclavicular joint (AC joint)

proximal component： convex lateral end of the clavicle

distal component： concave acromion process of the scapula

joint type： nearly plane joint

motion： shoulder girdle motion

scapular winging： medial border of the scapula moves backwards

scapular tipping： inferior angle of the scapula moves backwards

scapular upward/downward rotation： inferior angle of the scapula rotates upwards/downwards

DOF = 3

Joints at shoulder complex

Scapulothoracic articulation (ST articulation)

proximal component： convex rib cage

distal component： concave anterior surface of the scapula

NOTE： an articulation between bone and muscle; not a synovial joint

motion： shoulder girdle motion; convex on concave

scapular elevation/ depression： whole scapula moves upwards/ downwards

scapular abduction/ adduction： medial border of the scapula moves away from/ toward the spine

scapular upward/downward rotation： inferior angle of the scapula rotates upwards/downwards

DOF = 3

functions of the scapulothoracic articulation

to provide movement base for the humerus

to maintain length-tension relationship for the deltoid muscle to function above 90º of arm elevation

to provide stability of the GH joint working overhead

to absorb the shock for forces applied to the outstretched arm

to permit push-up during crutch walking

Joints at shoulder complex

Suprahumeral articulation

synonym： subacromial joint

coracoacromial arch： composed of the coracoacromial ligament

spraspinatus tendon passing underneath this arch

not for joint stability

shoulder impingement occurs if the subacromial space is insufficient

insufficient inferior glide of the humeral head during arm elevation

insufficient external rotation of the humerus during arm elevation

inflammation of the tendon of the supraspinatus

hypertrophy of the tendon of the supraspinatus

subacromial (subdeltoid) bursa

Joints at shoulder complex

Bicipital groove

groove between greater and lesser tuberosities of the humerus covered with the transverse humeral ligament

passing tendon of long head of biceps brachii

intra-articular but extra-synovial

Joints at shoulder complex

Plane of scapula

the plane at the angle of 30º anterior to the frontal plane

not parallel to the frontal plane

capsules in the loose-packed position

no impingement in the suprahumeral joint if shoulder motions occurs in the plane of scapula

Kinematics of the Shoulder Complex

Shoulder flexion and extension

joint involved

glenohumeral joint (principal joint)

sternoclavicular joint

acromioclavicular joint

scapulothoracic articulation

plane of motion： sagittal plane

axis of rotation： transverse axis through the center of the humeral head

osteokinematic movements

range of motion (ROM)

glenohumeral joint： 0-90º for shoulder flexion and 0-45º or 60º for shoulder extension

closed kinematic chain motions

pull-up (引體向上)

push-up (伏地挺身)

rowing

upper extremity cycling on an ergometer

arthrokinematic movements

posterolateral glide of the humeral head on the glenoid cavity with shoulder flexion

anteromedial glide of the humeral head on the glenoid cavity with shoulder extension

factors limiting shoulder flexion

inferior glenohumeral ligament (most important)

tightness of the posterior joint capsule

factors limiting shoulder extension

superior and middle glenohumeral ligament (most important)

Shoulder abduction and adduction

arm elevation = shoulder abduction or flexion

joint involved

glenohumeral joint (principal joint)

sternoclavicular joint

acromioclavicular joint

scapulothoracic articulation

plane of motion： frontal plane

axis of rotation

GH joint： sagittal axis through the center of the humeral head

SC joint： sagittal axis through the center of the medial end of the clavicle

osteokinematic movements

range of motion (ROM)

total range：0-165 or 175º

glenohumeral joint：0-120º of shoulder abduction

0-60º with full internal rotation of humerus

0-90º with full external rotation of humerus

sternoclavicular joint：0-30 or 45º

most occurring in 1^st 90º of arm elevation

scapulohumeral rhythm

Inman et al. (1944)

GH: ST = 2:1 after 30º of abduction

measured frontal plane motion

Bagg and Forrest (1988)

GH: at the beginning and the end

ST: 80-140 º of abduction

averaged ratio: 1.25:1

measured plane of scapula motion

Codman's paradox： conjunct rotation occurs during sequential motion

standing with dependent arm position with the palm of the hand facing medially and the thumb facing anteriorly ® shoulder flexion of 180º ® shoulder adduciton of 180º ® the thumb faces posteriorly

arthrokinematic movements

shoulder abduction

inferior glide of the humeral head on the glenoid cavity

inferior glide of the clavicle on the sternum in most people

factors limiting shoulder abduction

inferior glenohumeral ligament (most important)

tightness of the inferior joint capsule of the glenoumeral joint

tightness of the costoclavicular and interclavicular ligaments and the subclavicius muscles at the SC joint

factors limiting shoulder adduction

trunk

Shoulder internal/ external rotation

joint involved

glenohumeral joint (principal joint)

sternoclavicular joint

acromioclavicular joint

scapulothoracic articulation

plane of motion： transverse plane

axis of rotation： vertical axis through the center of the humeral head

osteokinematic movements

range of motion (ROM)

shoulder internal rotation： 0-70º as the arm at 90º of shoulder abduction and 90º elbow flexion

shoulder external rotation： 0-90º as the arm at 90º of shoulder abduction and 90º elbow flexion

Note： If the elbow is extended, shoulder rotation occurs simultaneously with forearm rotation.

arthrokinematic movements

posterolateral glide of the humeral head on the glenoid cavity with shoulder internal rotation

anteromedial glide of the humeral head on the glenoid cavity with shoulder external rotation

factors limiting shoulder internal rotation

posterior capsule

factors limiting shoulder external rotation

coracohumeral ligament

3 glenohumeral ligaments

Shoulder horizontal abduction/ horizontal adduction

synonym： horizontal extension/ flexion

shoulder flexion/ extension at 90º of shoulder abduction

horizontal abduction： arm moves backward as the arm is at 90º of shoulder abduction

horizontal adduction： arm moves forward as the arm is at 90º of shoulder abduction

joint involved

glenohumeral joint (principal joint)

sternoclavicular joint

acromioclavicular joint

scapulothoracic articulation

plane of motion： transverse plane

axis of rotation： vertical axis through the center of the humeral head

arthrokinematic movements

anteromedial glide of the humeral head on the glenoid cavity with shoulder horizontal abduction

posterolateral glide of the humeral head on the glenoid cavity with shoulder horizontal adduction

Frontal plane motions at shoulder girdle

shoulder girdle elevation

definition： ST joint elevation associated with SC elevation and AC tipping

joint involved

scapulothoracic articulation

sternoclavicular joint

acromioclavicular joint

arthrokinematic movement

elevation of the scapula on the rib cage

inferior glide of the clavicle on the sternum in most people

limited by the costoclavicular and interclavicular ligaments and the subclavicius muscle

shoulder girdle depression

important for crutch walking

definition： ST joint depression associated with SC depression

joint involved

scapulothoracic articulation

sternoclavicular joint

acromioclavicular joint

range： 10-15 cm from maximum scapular elevated position

arthrokinematic movements

depression of the capula on the rib cage

superior glide of the clavicle in most people

limited by first rib

Transverse plane motions at shoulder girdle

protraction definition： ST joint abduction associated with SC protraction joint involved scapulothoracic articulation sternoclavicular joint axis of rotation： vertical axis passing through the center of the medial head of the clavicle range 0-15º abduction of scapula：13-15 cm arthrokinematic movements abduction of the scapula protraction of the clavicle
limited by posterior sternoclavicular and costoclavicular ligaments
retraction definition： ST joint adduction associated with SC retraction joint involved scapulothoracic articulation sternoclavicular joint axis of rotation： vertical axis passing through the center of the medial head of the clavicle range：0-15º arthrokinematic movements adduction of scapula retraction of clavicle limited by anterior sternoclavicular ligament total range： 25º totally

Circumduction motions at the SC joint

A combination of elevation, protraction, depression, and retraction or in the reversed sequence

SC joint as the pivot

tip of shoulder (acromion process of the scapula) moves in a circle path

Scapulothoracic Rotation

upward rotation definition： glenoid fossa facing upwards with inferior angle of scapula sliding laterally and anteriorly osteokinematic movements fisrt 30º： elevation of the clavicle through the axis at the base of the spine of scapula last 30º： posterior rotation of the clavicle and scapular rotation around AC joint
downward rotation definition： glenoid fossa facing downwards with inferior angle of scapula sliding medially and posteriorly total range: 60º

Transverse rotation of clavicle

axis of rotation： longitudinal axis of the clavicle

total range: 40º

occurring after 90º of arm elevation due to tightening of the coracoclavicular ligament

arm elevation limited to 110º if this posterior rotation is not taken place

Muscles at the Shoulder Complex

The muscle at the shoulder complex act together as a team to produce highly coordinated motions.

Muscles for glenohumeral (shoulder) motions

motion	prime movers
shoulder flexion	deltoid, anterior fibers coracobrachialis biceps brachii, long head pectoralis major, clavicular head
shoulder extension	latissimus dorsi teres major triceps brachii, long head deltoid, posterior fibers
shoulder abduction	deltoid supraspinatus biceps brachii, long head
shoulder adduction	pectoralis major latissmus dorsi teres major triceps brachii, long head deltoid, posterior fibers
shoulder external rotation	infraspinatus teres minor deltoid, posterior fibers
shoulder internal rotation	subscapularis teres major pectoralis major latissimus dorsi deltoid, anterior fibers

Muscles for scapulothoracic (shoulder girdle) motions

motion	prime movers	motion	prime movers
scapular elevation	upper trapezius levator scapulae rhomboid major rhomboid minor	scapular depression	pectoralis minor lower trapezius latissmus dorsi subclavius
scapular protraction	serratus anterior pectoralis major pectoralis minor	scapular retraction	trapezius rhomboid major rhomboid minor
scapular upward rotation	trapezius serratus anterior	scapular downward rotation	levator scapula rhomboid major rhomboid minor

Serratus anterior

saw muscle

origin： rib 1-9

insertion： medial border of the scapula

motion： protraction + upward rotation

winging scapula if paralyzed

displacement of medial border of the scapula

Rotator cuff muscle

supraspinatus

infraspinatus

teres minor

subscpularis

Pectoralis minor

origin： rib 2-5

insertion： coracoid process of the scapula

depression + downward rotation

agonists

depressors

downward rotators

antagonists：

elevation + upward rotation

stablizers

neutralizers

for pure depression motion：

for pure downward rotation motion：

Important coupled muscles

levator scapula

latissimus dorsi

pectoralis major

trapezius: upper, middle, and lower

rhomboid major and minor

Shoulder Complex Stability

Factors affecting stability of the glenohumeral joint： primarily dependent on muscles and ligaments

bony configuration 5º of superior inclination (upward tilt) of the glenoid cavity shape of cartilage deepened glenoid labrum
tension of ligaments superior glenohumeral ligament middle glenohumeral ligament inferior glenohumeral ligament coracohumeral ligament muscular arrangement： rotator cuff supraspinatus infraspinatus teres minor subscapularis capsule

Mechanism of Injury at the Shoulder

Direct stress

direct stress à acromioclavicular (AC) joint separation

anterior stress à anteroinferior dislocation of the humeral head

Repeated stresses

repeated shoulder rotation motions as the shoulder is placed at 90º of abduction à repeated tensile stress on rotator cuff à rotator cuff tendinitis

Muscle paralysis

repeated shoulder rotation motions as the shoulder is placed at 90º of abduction à repeated tensile stress on rotator cuff à rotator cuff tendinitis

Established on 11/19/2002 and Last Updated 12/02/2004