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The Shoulder Complex

Functions of the Shoulder Complex
Structure of the Shoulder Complex
Kinematics of the Shoulder
Muscles at the Shoulder
Shoulder Stability
Mechanism 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 elbow 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 that of weakness of any single muscle on force generation

  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 L.K., Weiss E.L., Don Lehmkuhl L. (1996). Brunnstrom's Clinical Kinesiology, 5th ed. Philadelphia: FA Davis. Chapter 5
  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: mainly dependent on muscles (rotator cuff muscles) and ligaments 
  • To provide mobility of the arm in space: the greatest mobility in the body
  • To provide stability for elbow and hand skillful or forceful movements
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    Structure of the Shoulder Complex

     

    Articulations within the shoulder complex

  • glenohumeral joint: shoulder joint
  • sternoclavicular joint
  • acromioclavicular joint
  • scapulothoracic articulation
    muscle-bone articulation
  • 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
  • Articulation
    Elbow Flexion/ Extension

     

    Glenohumeral 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 medial-lateral axis at the elbow joint
  • joint type: ball-and-socket joint (Note: not a real socket)

  • motion:convex on concave
  • shoulder flexion/ extension with posterior/ anterior glide of the humeral head
  • shoulder abduction/ adduction with inferior/ superior glide of the humeral head
  • shoulder internal/ external rotation with posterior/ anterior glide of the humeral head
  • DOF = 3
  • rest position: 70° of shoulder flexion and 30° of flexion (horizontal adduction)
  • closed packed position: 90° of shoulder abduction and full external rotation
  • Articulation within Shoulder Complex
    Elbow Flexion/ Extension

     

    Sternoclavicular joint

  • proximal component: sternum
  • saddle-shaped manubrium sterni
  • distal component: clavicle
  • saddle-shaped medial end of the clavicle
  • articular disc between 2 articular surfaces
  • joint type: saddle joint
  • movements: shoulder girdle motion
  • clavicle elevation/ depression
  • clavicle protraction/ depression
  • clavicle posterior rotation
  • DOF = 3
    Note: It is a 3-degree-of-freedom saddle joint.
  • 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
  • Articulation within Shoulder Complex
    Elbow Flexion/ Extension

     

    Acromioclavicular joint

  • proximal component: convex lateral end of the clavicle
  • distal component: concave acromion process of the scapula
  • joint type: nearly plane joint (sometimes slightly concave or slightly convex)
  • movements
  • upward/ downward rotation
  • winging (horizontal plane adjustment)
  • tipping (sagittal plane adjustment)
  • DOF = 3
  • Articulation within Shoulder Complex
    Elbow Flexion/ Extension

     

    Scapulothoracic articulation

  • proximal component: convex rib cage
  • distal component: concave anterior surface of the scapula
  • Note: not a real anatomical joint
  • movements at the scapulothoracic articulation are the results of movements occurring at the sternoclavicular and acromioclavicular joints
  • elevation/ depression
  • protraction/ retraction
  • upward/ downward rotation
  • Articulation within Shoulder Complex
    Elbow Flexion/ Extension

     

    Suprahumeral articulation

  • 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
  • Articulation within Shoulder Complex
    Elbow Flexion/ Extension

     

    Bicipital groove (intertubercular groove)

  • groove between greater and lesser tubercles of the humerus where the tendon of the long head of the biceps brachii passes.  The roof of the groove is covered with transverse humeral ligament.
  • During shoulder motions, the humeral head slides on the undersurface of the tendon of the long head of the biceps brachii
  • intra-articular but extra-synovial
  • Articulation within Shoulder Complex
    Elbow Flexion/ Extension

     

    Plane of scapula

  • not parallel to the frontal plane
  • the plane at the angle of 30º anterior 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
  •  

    Dependent arm position

  • the position that the arm is hanging down by the side of the trunk
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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 of shoulder flexion and 0-45º or 60º of 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
  • 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
  • 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
  • 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/ adduction

  • 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
  • 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

  • elevation:30-45º
  • most occurring in 1st 90º of arm elevation
  • with inferior glide in most people
  • limited by the costoclavicular and interclavicular ligaments and the subclavicius muscle
  • depression:5-10º
  • important for crutch walking
  • 10-15º of depression from resting position
  • 10-15 cm from maximum scapular elevated position
  • with superior glide in most people
  • limited by first rib
  •  

    Transverse plane motions at shoulder girdle

  • protraction:15º
  • abduction of scapula: 13-15 cm
  • protraction of clavicle
  •  limited by posterior sternoclavicular and costoclavicular ligaments
  • retraction:15º
  • adduction of scapula
  • retraction of clavicle
  • limited by anterior sternoclavicular ligament
  • total range: 25º totally
  •  

    Circumduction motions at shoulder girdle

  • A combination of elevation, protraction, depression, and retraction or in the reversed sequence
  • SC joint as the pivot
  • tip of shoulder moves in a circle path
  •  

    Rotation of shoulder girdle

  • upward rotation
  • glenoid fossa facing upwards
  • inferior angle of scapula slides laterally and anteriorly
  • downward rotation
  • glenoid fossa facing downwards
  • inferior angle of scapula slides 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 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

  • 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 that stabilize the glenohumeral joint

  • bony configuration: not important
  • 5º of superior inclination (upward tilt) of the glenoid cavity
  • shape of cartilage
  • glenoid labrum: to contribute 50% of overall depth of the glenoid cavity
  • tension of ligaments

    ligament shoulder motions
    to pull the ligament taut
    humeral head motion
    to pull the ligament taut
    superior glenohumeral lig. full adduction inferior or anterior glide
    middle glenohumeral lig. external rotation anterior glide
    inferior glenohumeral lig.
          anterior band
          posterior band

    abduction and external rotation
    abduction and internal rotation
    non specific
    coracohumeral lig. extremes of flexion, extension, or external rotation inferior glide
  • muscular arrangement: rotator cuff
  • supraspinatus
  • infraspinatus
  • teres minor
  • subscapularis
  • capsule: not important
  •  

    Factors that stabilize the sternoclavicular joint

  • bony configuration: saddle shaped
  • shape of cartilage
  • interarticular disc to increase the congruity of the irregular articular surface
  • tension of ligaments:
  • costoclavicular ligament (most important)
  • anterior sternoclavicular ligament
  • posterior sternoclavicular ligament
  • interclavicular ligament
  • muscular arrangement:
  • strenal head of the sternocleidomastoid muscle (anterior)
  • sternothyroiod and sternhyoid muscles (posterior)
  • capsule
  •  

    Factors that stabilize the acromioclavicular joint

  • bony configuration: flat shaped
  • shape of cartilage
  • fibrocartilage with a articular disc
  • tension of ligaments:
  • superior acromioclavicular ligament
  • inferior acromioclavicular ligament
  • coracoclavicular ligament: conoid (medial) and trapezoid ligaments (lateral)
  • muscular arrangement:
  • deltoid
  • trapezius
  • capsule
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    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
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    Established on 11/19/2002 and Last Updated 11/11/2005 © 2004 Huei-Ming Chai, PhD PT          All Right Reserved