The Shoulder Complex

Functions of the Shoulder ComplexStructure of the Shoulder ComplexKinematics of the Shoulder ComplexMuscles at the ShoulderShoulder StabilityMechanism of Injury at the Shoulder

　

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

1. to identify the structure of the shoulder and the shoulder girdle, including joint type, articular shape, and the surrounding tissues

2. to describe joint motions occurring at the shoulder complex, including osteokinematic and arthrokinematic movements, muscle actions, and factors checking shoulder motions

3. to understand the stability mechanism of the shoulder complex and the possible mechanisms of injury 4. to distinguish the three-degree-of-freedom joint from the one- or two-degree-of-freedom joint 5. to understand the effect of muscle synergies and the influence of weakness or paralysis of one single

muscle in coupled-muscle motions

1. Neumann DA (2002).  Shoulder complex.  In Neumann DA: Kinesiology of the Musculoskeletal System: Foundations for Physical Rehabilitation. Philadelphia: Mosby.  Chapter 5, pp. 91-132

2. Smith LK, Weiss EL, Don Lehmkuhl L (eds, 1996). Brunnstrom's Clinical Kinesiology, 5th ed.  Philadelphia, F.A. Davis.  Chapter 5, pp. 223-225

3. 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

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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 sternocl

avicular 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

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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 1st 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

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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 fiberscoracobrachialisbiceps brachii, long headpectoralis major, clavicular head

shoulder extension

latissimus dorsiteres majortriceps brachii, long headdeltoid, posterior fibers

shoulder abductiondeltoidsupraspinatusbiceps brachii, long head

shoulder adduction pectoralis majorlatissmus dorsiteres majortriceps brachii, long head

deltoid, posterior fibers

shoulder external rotationinfraspinatusteres minordeltoid, posterior fibers

shoulder internal rotation

subscapularisteres majorpectoralis majorlatissimus dorsideltoid, anterior fibers

　

Muscles for scapulothoracic (shoulder girdle) motions

motion prime movers motion prime movers

scapular elevation

upper trapeziuslevator scapulaerhomboid majorrhomboid minor

scapular depression

pectoralis minorlower trapeziuslatissmus dorsisubclavius

scapular protractionserratus anteriorpectoralis majorpectoralis minor

scapular retractiontrapeziusrhomboid majorrhomboid minor

scapular upward rotationtrapeziusserratus anterior

scapular downward rotationlevator scapularhomboid majorrhomboid 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

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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

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Mechanism of Injury at the Shoulder

　

Direct stress

direct stress   acromioclavicular (AC) joint separation anterior stress   anteroinferior dislocation of the humeral head

　

Repeated stresses

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

　

Muscle paralysis

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