Gross Anatomy
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THE SHOULDER GIRDLE

Required Reading : pages 310 -329

I. INTRODUCTION

  1. The shoulder or pectoral girdle consists of articulations between the clavicle, scapula and the proximal end of the humerus. The sternoclavicular articulation is the only bony link between the upper limb and the axial skeleton. Movements at this joint are largely passive in that the occur as a result of active movements of the scapula. Through the acromioclavicular articulation, the clavicle can act as a strut maintaining the upper limb away from the thorax permitting a greater range of upper limb motion. This joint also helps provide static stability to the upper limb reducing the need to use muscle energy to keep the upper limb in its proper alignment. The glenohumeral articulation (shoulder joint) has the greatest range of motion of any joint in the body. The mobility of the shoulder joint is necessary for placement of the hand to maximize manipulation. The scapula is suspended on the thoracic wall by muscle forming a "functional joint" called the scapulothoracic joint. These muscles act to stabilize and/ or to actively move the scapula. Active movements of the scapula help increase the range of motion of the shoulder joint.
  2. The student will be asked to demonstrate their understanding of shoulder girdle anatomy by applying this information in the diagnosis of problems of these often injured joints

II. COMPONENTS OF THE SHOULDER GIRDLE (310 -317)

  1. Bones
    1. Clavicle
    2. Scapula
    3. Proximal end of humerus
  2. Articulations
    1. Acromioclavicular Joint
      1. Planar type joint between lateral portion of the clavicle and the acromion of the scapula.
    2. Sternoclavicular Joint
      1. Sellar joint between the medial end of the clavicle and the manubrium of the sternum.
    3. 3. Glenohumeral ( Shoulder ) Joint
      1. Ball and socket articulation between head of humerus and glenoid cavity.
      2. Favors mobility over stability
    4. Scapulothoracic "Joint"
      1. Scapula suspended on rib cage by muscles
        1. highly mobile
      2. capula movements increases range of motion at the shoulder joint

III. MUSCLES ACTING ON THE SHOULDER GIRDLE (pgs. 322-326)

  1. Extrinsic - Suspend scapula from the trunk .Stabilize and/or actively moves scapula
    1. Trapezius
    2. Levator Scapulae
    3. Rhomboid Major and Minor
    4. Serratus Anterior
    5. Pectoralis minor
  2. Intrinsic - Attach scapula to humerus
    1. Deltoid
    2. Teres Major
    3. Rotator Cuff (active stabilization of shoulder joint)
      1. Supraspinatus
      2. Infraspinatus
      3. Teres Minor
      4. Subscapularis
  3. Attach trunk to humerus
    1. Latissimus dorsi
    2. Pectoralis Major
  4. Attachments and Functions (See Chart 1)

IV. STABILITY OF THE SHOULDER GIRDLE (pgs 318 -321)

  1. Acromioclavicular Joint
    1. Ligaments
      1. Acromioclavicular
      2. Coracoclavicular
      3. Conoid
      4. Trapezoid
    2. 2. Functions
      1. Bind clavicle to scapula supporting weight of upper limb minimizing use of muscle energy
    3. 3. Shoulder Separation
      1. Tearing of acromioclavicular and /or coracoclavicular ligaments
      2. Clavicle overrides acromion
      3. Weight of upper limb pulls scapula and acromion inferiorly below clavicle
  2. Sternoclavicular Joint
    1. Ligaments
      1. Sternoclavicular
      2. ianterior and posterior
      3. Interclavicular
      4. Costoclavicular
    2. Fibrocartilage Disc
      1. Strengthens articulation
  3. Glenohumeral Joint
    1. Capsule
      1. Attaches from glenoid cavity to anatomical neck of humerus
      2. Least amount of support inferiorly
    2. Ligaments
      1. Coracoacromial
        1. Helps resist upward displacement of the head of the humerus
      2. Coracohumeral
        1. Strengthens superior portion of capsule
        2. Some support during shoulder abduction
      3. Transverse Humeral Ligament
        1. holds long head of biceps in the groove
      4. Glenohumeral Ligaments - 3 parts all attach from upper margin of glenoid cavity and strengthen anterior portion of capsule
        1. Superior - over the humeral head to a depression above the lesser tuberosity
        2. Middle - in front of humerus to lower lesser tuberosity
        3. Inferior - to lower part of the anatomical neck
    3. Rotator Cuff Muscles
      1. Active stabilizers of shoulder joint
        1. act throughout entire range of motion at shoulder
      2. Depress head of humerus in glenoid cavity when humerus moves
        1. Prevents compression of structures between humeral head and acromion
      3. Muscles also help rotate shoulder (See Chart: "Movements of Glenohumeral Joint" )
  4. D.Scapulothoracic Articulation
    1. 1. Stability
      1. Dependent upon activity of extrinsic muscles
      2. Winged scapula
    2. 2. Alignment
      1. Upwardly rotated and elevated position of scapula at rest
        1. action of trapezius muscle

V. MOVEMENTS OF THE STERNOCLAVICULAR JOINT

  1. Passive movements.
    1. Acromial end moves as consequence of movements of the scapula
    2. Sternal end of clavicle moves in a direction opposite from that of the scapula.
  2. Types of Movements
    1. Protraction - scapula is retracted causing the sternal end to move forward
    2. Retraction - scapula is protracted causing the sternal end to move backward
    3. Elevation - scapula is depressed causing the sternal end to move upward
    4. Depression - scapula is elevated causing the sternal end to move downward
  3. Muscles Acting on Sternoclavicular Joint
    1. The muscles acting on the Sternoclavicular joint are outlined in Chart 1. These are the same muscles that act on the scapula.
    2. Movements of the Sternoclavicular joint and the muscles producing these movements are outlined in Chart 2. Remember the SC joint moves in a direction opposite from the way in which the scapula moves.

VI. MOVEMENTS OF THE SCAPULA ( pg 316)

  1. Types
    1. Elevation - moving the superior border of the scapula and the acromion in an upward direction.
    2. Depression - moving the superior border of the scapula and the acromion in an downward direction.
    3. Upward Rotation - Moving the scapula so that the glenoid cavity faces upward.
      1. Increased the ranges of motion during abduction and/or flexion of the shoulder.
    4. Downward Rotation - moving the scapula so that the glenoid cavity faces inferiorly.
      1. Increases range of motion during extension and / or adduction of the shoulder.
    5. Protraction ( Abduction) - moving the scapula away from the midline
    6. Retraction (Adduction) - moving the scapula toward the midline
  2. Muscles Acting to Move Scapula
    1. Very mobile
      1. Muscles suspend scapula from vertebral column and chest wall
      2. Axis around which scapulae move changes
      3. Muscles attach to scapula obliquely
        1. Produce many motions
    2. Movements
      1. See chart Movements of the Scapula
    3. Muscle Synergy at the Shoulder Joint
      1. Retraction of the Scapula
        1. Trapezius -- retract and rotates upward
        2. Rhomboids -- retract and rotate downward
      2. Upward rotation of the Scapula
        1. Serratus anterior -- protracts and rotates upward
        2. Trapezius -- Retract and rotates upward

VII. MOVEMENTS OF THE GLENOHUMERAL JOINT ( pgs 322-323)

  1. Properties
    1. Movements of the shoulder joint (glenohumeral joint) usually involve moving the humerus on the scapula.
    2. All movements are to be studied starting from the ANATOMICAL POSITION
    3. Axis of motion
      1. Flexion - Extension
        1. Coronal axis through head of humerus
      2. Abduction /Adduction
        1. Sagittal axis through humeral head
      3. Rotation
        1. Longitudinal axis through shaft of humerus
  2. Types of Movements
    1. Flexion moving the humerus forward and upward in the sagittal plane.
    2. Extension - bringing the arm down to the side in the sagittal plane.
      1. Hyperextension - moving the arm in the sagittal plane behind the body.
    3. Abduction - moving the arm in the coronal plane away from the midline
      1. Stages
        1. initiate -supraspinatus
        2. 900 - deltoid
        3. 1800 - deltoid with upward rotation of scapula
    4. Adduction - moving the arm in the coronal plane towards the midline.
    5. Inward Rotation - rotating the arm in a transverse plane so that the anterior surface of the bone turns inward.
    6. Outward Rotation - rotating the arm in a transverse plane so that the anterior surface of the bone turns outward.
  3. Scapulohumeral Rhythm
    1. Coordinated movements of the scapula and the humerus increasing the range of motion at the glenohumeral joint
      1. Most noticeable during complete flexion and abduction of the shoulder
      2. 2 - 30 of humeral abduction is associated with 1 - 20 of scapula rotation
  4. Movements of the Shoulder Joint
    1. Chart 3 - MOVEMENTS of the SHOULDER JOINT indicates which muscles interact to produce a given movements of the shoulder

VIII. CLINICAL ANATOMY OF THE SHOULDER JOINT ( pgs. 317,319,321)

  1. Dislocation
    1. Weakness of rotator cuff tendons and / or trauma
    2. Head of humerus subluxes (separated ) from glenoid cavity of humerus
    3. Usually occurs when humerus is in position of abduction or flexion
      1. Least amount of contact between apposing bony surfaces
    4. Occurs in an inferior direction
      1. Weakest region of capsule
      2. Humerus pulled either anterior to or posterior to shoulder joint depending upon which rotator cuff muscles are injured.
    5. Arm hangs limp at side with a prominent "step deformity" (space) between acromion and humeral head
  2. Impingement Syndrome
    1. Weakness or fatigue of rotator cuff muscles
    2. Activity of shoulder joint accompanied by intense pain
      1. Movements of abduction and flexion usually more painful
      2. Painful arc
        1. Very painful abducting from neutral position to horizontal. Then pain subsides
    3. Compression of supraspinatus tendon between head of humerus and acromion.
  3. Nerve Lesions (pg 329)
    Lesions to components of the brachial plexus, especially those components associated with the C 5 and/or C 6 nerve roots, will have and major effect on the ability of the shoulder girdle to carry out normal functions. Often, the signs and symptoms concerning loss or reduction in function can be used to localize the site of the nerve lesion. The effects of various types of nerve lesions can have on the shoulder girdle is summarized below:
    1. Accessory nerve - innervates the trapezius muscle. Paralysis of this muscle will result in a marked drooping and down turning of the affected shoulder at rest because of the loss of the ability of the trapezius to elevate and upwardly rotate the scapula. The latter loss will also prevent the patient from abducting their arm above the horizontal ( shoulder level).
    2. Dorsal Scapular nerve - innervates the rhomboideus muscles. Any attempt to retract the scapula will be accompanied by a marked upward rotation of the shoulder because the rhomboideus can no oppose the upward rotation on the scapula exerted by the trapezius. The patient will have difficulty retracting the scapula against resistance on the affected side.
    3. Long thoracic nerve - Innervates the serratus anterior muscle. Active contraction of this muscle results in scapula protraction and upward rotation. When the scapula is passively protracted by action of the pectoralis major muscle on the humerus , the serratus anterior acts to stabilize the scapula and keep it applied to the thoracic wall. Such action occur when a boxer throws a jab or a cross. Paralysis of the serratus anterior prevents the scapula from moving smoothly across the thoracic wall resulting in a bowing out of the medial border of the scapula. This condition is called "winged" scapula. In addition, the ability to actively upwardly rotate the shoulder is diminished and the patient can not abduct the humerus above the horizontal.
    4. Suprascapular nerve - innervates the supraspinatus and infraspinatus muscles. Paralysis of this nerve will result is weakness of the rotator cuff muscles resulting in pain form impingement and an inability of the patient to begin shoulder abduction. Such patients tend to swing the affected limb away from their side in order to provide momentum to start abduction.
    5. Axillary nerve - innervates the deltoid and teres minor muscles. Since the deltoid plays a major role in movement of the glenohumeral joint, paralysis will cause a loss &/or weakness of most shoulder functions. Symptoms of deltoid paralysis include:
      1. loss or roundness to the shoulder and a very visible acromion process
      2. inability to abduct the glenohumeral joint more than a few degrees away from the side.
      3. inability to laterally rotate the humerus
      4. weakened movements of glenohumeral flexion and extension
      5. loss of sensation just below the point of the shoulder
    6. C5, C6 root damage ( Erb's palsy) - axons from the C5 and C6 ventral rami innervate the following muscles acting on the shoulder girdle:
      deltoid, supraspinatus, infraspinatus , teres minor, subscapularis. Lesion to these roots will result in paralysis of these muscles. The symptoms of such a lesion are outlines in the chart below.


C5, C6 Nerve Root Lesion (Erb's Palsy)

MOTOR DEFICITS SENSORY DEFICIT NERVES
Loss of abduction, flexion and rotation at shoulder ; Weak shoulder extension - deltoid, rotator cuff Posterior and lateral aspect of arm - axillary n. Axillary, Suprascapular, Upper and Lower subscapular
Very weak elbow flexion and supination of radioulnar joint- biceps brachii & brachialis Radial side of Forearm- musculocutaneous n. Thumb and 1st finger - superficial br. of radial; digital brs. - Median n. Musculocutaneous ; Radial N. brs. to supinator & brachioradialis muscles
Susceptible to shoulder dislocation - loss of rotator cuff muscles
Suprascapular, Upper and Lower subscapular
"Waiters Tip"position




Chart 1 - Muscles Acting On The Shoulder Girdle

MUSCLE PROXIMAL DISTAL NERVE FUNCTIONS
Extrinsic: Attach scapula to neck and trunk
Trapezius 1. Ext Occipital Protuberance

2. Lig . nuchae

3. Lower cervical & thoracic spines

1. Lat. 1/3 of clavicle (upper)

2. Acromion (middle)

3. Spine of scapula (lower)

Spinal portion of XI Retracts and upwardly rotates scapula
Levator Scapulae Transverse processes of C 1 to or 4 Upper medial border of the scapula Cervical Plexus

C 3 & C 4

Elevation and downward rotation of the scapula
Rhomboid Major & Minor 1. Ligamentum nuchae,

2. spinous processes of C7 to T 5

Medial border of the scapula; from the root of the spine to the inferior angle Dorsal Scapular

(Nerve to Rhomboids)

C 4; (C5)

1. Retraction, downward rotation, some elevation of the scapula,

2. Fixes the scapula against the trunk

Serratus Anterior Outer surface of ribs

1-8

Anterior surface of the medial border of the scapula Long Thoracic

( C 5,6,7)

1.Protraction and upward rotation of scapula

2. Fixes scapula against the thoracic wall

Pectoralis Minor Ribs 3, 4, & 5 Coracoid process of scapula Medial Pectoral Nerve (C8,T1) Protract, downward rotation o f scapula
Intrinsic: Rotator Cuff ( Active stabilization of shoulder joint by preventing downward displacement of the humerus)
Supraspinatus Supraspinous fossa of scapula Superior facet of the greater tubercle of humerus Suprascapular

(C 5,6)

Starts shoulder abduction
Infraspinatus Infraspinous fossa of scapula Middle facet of the greater tubercle of humerus Suprascapular

(C 5,6)

Lateral shoulder rotation
Teres Minor Lateral border of scapula, superior to Teres Major Inferior fact of the greater tubercle of the humerus Axillary (C 5,6) Lateral shoulder rotation

MUSCLE PROXIMAL DISTAL NERVE FUNCTIONS
Subscapularis Subscapular fossa of the scapula Lesser tubercle of humerus Subscapular Nerves (C 5,6) 1. Medial shoulder rotation
Intrinsic: Attach humerus to scapula
Deltoid 1. Lateral one third of clavicle

2. Acromion

3. Spine of the scapula

Deltoid tuberosity

on the humeral shaft

Axillary (C 5,6) Anterior portion - flexes, medially rotates shoulder

Middle portion - abducts the shoulder

Posterior Portion - extends, laterally rotates the shoulder

Teres major Dorsal scapula near inferior angle Crest of the lesser tubercle of humerus Lower Subscapular

(C 5,6)

1. Adduction and medial rotation of the shoulder

2. Stabilizes shoulder during abduction

3. Extend shoulder from flexed position

Attach humerus to trunk ( Act primarily on humerus; scapula moves passively in response to movement of humerus)
Latissimus Dorsi 1. Thoracolumbar fascia

2. Sacrum, iliac crest

3. Spinous processes of T 6 to L5

Floor of bicipital groove (also called intertubercular sulcus) Thoracodorsal

(C 6,7,8)

1.Extend, Adduct, and Medially rotate the shoulder

2. Depress and downward rotation of scapula

Pectoralis Major 1. Medial 1/2 of the clavicle

2. Sternum, costal cartilages of ribs 2 6

Lateral lip of the bicipital groove (also called the intertubercular sulcus) Lateral and Medial Pectoral nerves (C6-T1) 1. Adduction, Flexion, Medial Rotation of the shoulder

2. Horizontal Adduction

3. Protraction of scapula



Chart 2 - MOVEMENTS OF THE SCAPULA

Motion Prime Movers Nerve Critical Segment
Elevation Trapezius- upper Accessory
Levator scapulae N. to L. scapulae C 3,4
Rhomboideus major* Dorsal scapular C (4),5
Rhomboideus minor* Dorsal scapular C (4),5
Depression Latissimus dorsi1 Thoracodorsal C 7
Pectoralis major - sternal head1 Pectoral Nerves C 6, 7,8
Pectoralis minor Medial pectoral C 8, T1
Upward Rotation Serratus anterior Long thoracic C 5, 6, 7
Trapezius-Upper & Lower Accessory
Downward Rotation Latissimus dorsi1 Thoracodorsal C 7
Pectoralis major - sternal head1 Pectoral Nerves C 6, 7,8, 1
Pectoralis minor Medial pectoral C 8, T1
Levator scapulae N. to L. scapulae C 3,4
Protraction Serratus anterior Long thoracic C 5, 6, 7
Pectoralis minor Medial pectoral C 8, T 1
Pectoralis major 1 Pectoral Nerves C 6, 7,8, 1
Retraction Trapezius Accessory
Rhomboideus major Dorsal scapular C (4),5
Rhomboideus minor Dorsal scapular C (4),5

* When the rhomboids assist in elevation, the resultant movement is a combination of elevation and retraction.

1 Muscles passively move scapula through their active action on the humerus



Chart 3 -MOVEMENTS OF THE GLENOHUMERAL JOINT

Motion Prime Movers Nerve Critical Segments
Flexion Deltoid - anterior Axillary C 5
Pectoralis major - clavicular head Lateral Pectoral C 5, 6
Coracobrachialis* Musculocutaneous C 5, 6, 7
Extension Deltoid - posterior Axillary C 5
Latissimus dorsi Thoracodorsal C 7
Teres major Lower subscapular C 5, 6
Abduction Supraspinatus1 Suprascapular C 5, 6
Deltoid - anterior Axillary C 5
Adduction Latissimus dorsi Thoracodorsal C 7
Pectoralis major - sternal head Pectoral nerves C 6, 7, 8, 1
Inward Rotation Subscapularis Upper subscapular C 5, 6
Deltoid - anterior Axillary C 5
Outward Rotation Infraspinatus Suprascapular C 5, 6
Teres minor Axillary C 5
Deltoid - posterior Axillary C 5



Figure 1 SCAPULA MOVEMENTS
Retraction means the scapula is drawn towards the midline; protraction is movement away from the midline. Elevation is raising the entire scapula upwards as in shrugging ones shoulder; depression is lowering the scapula.



Figure 2 SCAPULA ROTATION
Upward Rotation of the scapula involves rotating the glenoid cavity upward while moving the inferior angle laterally; downward rotation involves rotating the glenoid cavity downward while the inferior angle moves medially. Upward rotation occurs during flexion and abduction of the shoulder to increase the range of motion when the humerus moves on the scapula. Downward rotation is used to increase the range of motion of the humerus when it moves on the scapula during shoulder extension and adduction.



Figure 3 Shoulder Girdle - Anterior
1. Name the bony features of the shoulder girdle indicated by each number

2. Draw in the ligaments the support the joints of the shoulder girdle




Figure 4. Shoulder Girdle - Posterior
1. Name the bony components of the shoulder girdle indicated by each number.

2. The dashed line is the __________________________________. What structure attaches here?

3. What are the names and functions of the muscles inserting at the dark rectangles?

4. What is the name and function(s) of the muscle inserting along the bones labeled 3, 4, 5?



IX. OBJECTIVES

  1. A Know the bones, supporting ligaments and function of the articulations that comprise the shoulder girdle
    1. Understand the primary factors that account for the stability of each joint
  2. B Understand the types of movements that can take place at the sternoclavicular and glenohumeral joints.
    1. Know the prime mover(s) for each type of movement
    2. Be able to distinguish between active and passive movements
  3. C Be familiar with the concept of the "scapulothoracic" joint
    1. Know the types of movements that can take place between the scapula and rib cage
    2. Be able to figure out the prime movers for each type of movement
    3. Be able to distinguish between active and passive movements of the scapula
      1. Give examples of how muscles act to "fix" or stabilize the scapula
      2. Be able to give examples of muscles acting synergistically on the scapula
    4. Define scapulohumeral rhythm
      1. Understand the importance of this rhythm in shoulder abduction
  4. Be able to distinguish between a shoulder separation and shoulder dislocation.
    1. Know what types of structures are damaged in each case
    2. Be able to distinguish between each injury based upon the resultant position that the limb will assume as a result of each type of injury
  5. Understand the anatomical basis of Impingement Syndrome
  6. Understand how nerve lesions of the following nerves will affect movements of the scapulothoracic and glenohumeral joints .
    1. Long thoracic nerve
    2. Suprascapular nerve
    3. Axillary nerve
    4. Thoracodorsal nerve
    5. C5 - C6 nerve roots
  7. Be prepared to demonstrate by testing the action(s) of the appropriate muscles how the above nerve lesions will affect movement of the scapula and / or humerus
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