Shoulder

Question 1

Anterior muscles of the pectoral region

• General innervation?
• What are the 3 anterior muscles?
• Origin, insertion, actions, and innervation?
• What causes a winged scapula and why?

Answer 1

Anterior muscles of the pectoral region

• Originate on the anterior aspect of the axial skeleton
• General innervation: C6-8

Pectoralis major (clavicular and sternocostal heads)

• Origin:
  
  • Clavicle
  • Sternum
  • Costal cartilages of superior ribs
• Insertion:
  
  • Anteriormedial aspect of proximal humerus
• Actions:
  
  • Adduction of GHJ
  • Flexion of GHJ
  • Medial rotation of GHJ
• Innervation:
  
  • Medial pectoral nerves
  • Lateral pectoral nerves

Pectoralis minor (does NOT cross GHJ)

• Origin:
  
  • Ribs 3-5
• Insertion:
  
  • Coracoid process of scapula
• Actions:
  
  • Protraction of scapula
  • Depression of scapula
  • Stabilizes scapula
• Innervation:
  
  • Medial pectoral nerve (Medial does more)

Serratus anterior (between scapula and thoracic wall)

• Origin:
  
  • Lateral aspect of ribs 1-8
• Insertion:
  
  • Anterior surface of medial border of scapula
• Actions:
  
  • Protraction of scapula
  • Upward rotation of scapula
  • Fixes scapula on thoracic wall
• Innervation:
  
  • Long thoracic nerve
    
    • Superficial to serratus anterior so it is open to injury
    • Lesion along the long thoracic nerve paralyzes the serratus anterior muscle, resulting in a winged scapula, as the scapula is no longer fixed to the thoracic wall

Question 2

Blood supply of the anterior pectoral region

• What is the axillary artery a continuation of?
• What are the two branches and what do they supply?
• What does the second artery course with?

Answer 2

Blood supply of the anterior pectoral region

• Axillary artery (continuation of the subclavian artery)
  
  • Thoracoacromial artery
    
    • Supplies pectoral mucles and deltoid
  • Lateral thoracic artery
    
    • Courses with the long thoracic nerve
    • Supplies serratus anterior and pectoral muscles

Question 3

Extrinsic muscles of the back (posterior)

• General innervation?
• What are the 5 extrinsic muscles of the back?
• Origin, insertion, actions, and innervation?

Answer 3

Extrinsic muscles of the back (posterior view)

• Originate on the posterior aspect of the axial skeleton
• General innervation: C5-7 and CN XI

Trapezius

• Origin:
  
  • Occipital bone
  • Nuchal ligament
  • Thoracic spinous processes
• Insertion:
  
  • Clavicle
  • Acromion
  • Spine of the scapula
• Actions:
  
  • Superior portion: elevation and upward rotation of the scapula
  • Middle portion: retraction of scapula
  • Inferior portion: depression and upward rotation of scapula
• Innervation:
  
  • CN XI

Levator scapulae

• Origin: cervical transverse processes
• Insertion: superior angle of the scapula
• Actions: elevation and downward rotation of scapula
• Innervation: dorsal scapular nerve

Rhomboid minor and major

• Origin:
  
  • Nuchal ligament
  • Thoracic spinous processes
• Insertion:
  
  • Medial border of scapula
• Actions:
  
  • Retraction and downward rotation of scapula
  • Fixes scapula to body wall
• Innervation:
  
  • Dorsal scapular nerve (innervates 3 muscles total)

Latissimus dorsi

• Origin:
  
  • Thoracolumbar fascia
  • Iliac crest
  • Ribs
• Insertion:
  
  • Anteriormedial aspect of proximal humerus
• Actions:
  
  • Extension of GHJ
  • Adduction of GHJ
  • Medial rotation of GHJ
• Innervation:
  
  • Thoracodorsal nerve

Question 4

Intrinsic muscles of the shoulder (posterior view)

• Generally originates and inserts on?
• General innervation?
• What are the intrinsic muscles of the shoulder? (In addition to rotator cuff muscles)
• Origin, insertion, actions, and innervation?
• What are two tests to test for axillary lesion?

Answer 4

Intrinsic muscles of the shoulder (posterior view)

• Originate on the scapula and insert on the humerus
• General innervation: C5-6

Deltoid (does everything with GHJ except adduct!)

• Origin:
  
  • Clavicle
  • Acromion
  • Spine of scapula
• Insertion:
  
  • Deltoid tuberosity of humerus
• Actions:
  
  • Anterior portion: flexion and medial rotation of GHJ
  • Middle portion: abduction after 15 degrees of GHJ
  • Posterior portion: extension and lateral rotation of GHJ
• Innervation:
  
  • Axillary nerve
    
    • Lesion of the axillary nerve can be tested by palpation of the deltoid muscle while abducting against resistance after 15 degrees. Patient will also have loss of skin sensation on lateral aspect of shoulder.

Teres major (most inferior of all the instrinsic shoulder muscles)

• Origin:
  
  • Inferior angle of the scapula
• Insertion:
  
  • Anteriormedial aspect of the proximal humerus
• Actions:
  
  • Medial rotation of GHJ
  • Adduction of GHJ
• Innervation:
  
  • Lower subscapular nerve

Question 5

Rotator cuff muscles (part of intrinsic muscles of the shoulder)

• What are the rotator cuff muscles?
• Origin, insertion, actions, and innervation?

Answer 5

Rotator cuff muscles (part of intrinsic muscles of the shoulder)

• SITS
• Creates a supportive musculotendinous cuff around the GHJ and helps to stabilize it

Supraspinatus

• Origin: supraspinous fossa of scapula
• Insertion: greater tubercle of humerus
• Actions: abduction of GHJ to 15 degrees and stabilize GHJ
• Innervation: suprascapular nerve

Infraspinatus

• Origin: infraspinous fossa of scapula
• Insertion: greater tubercle of humerus
• Actions: lateral rotation of GHJ and stabilize GHJ
• Innervation: suprascapular nerve

Teres minor

• Origin: lateral border of scapula
• Insertion: greater tubercle of humerus
• Actions: lateral rotation of GHJ and stabilize GHJ
• Innervation: axillary nerve

Subscapularis

• Origin: subscapular fossa of scapula
• Insertion: lesser tubercle of humerus
• Actions: medial rotation and adduction of GHJ, and stabilize GHJ
• Innervation: upper and lower subscapular nerves

Question 6

Blood supply of the posterior shoulder

• Subclavian artery gives rise to?
• What are the two branches of this artery?
  
  • What does the first branch branch into and what do they supply?
  • What does the second branch supply? What does this artery course over, and what courses under?
• What is the vein exception?
• What is the flow of drainage for the posterior shoulder?

Answer 6

Blood supply of the posterior shoulder

• Subclavian artery gives rise to the thyrocervical trunk
  
  • Transverse cervical artery
    
    • Superficial branch supplies trapezius
    • Deep branch (dorsal scapular artery) supplies rhomboids and levator scapulae (this branch may arise separately from the subclavian artery)
  • Suprascapular artery
    
    • Supplies supraspinatus and infraspinatus
    • Contributes to collateral circulation of the shoulder
    • This artery courses over the superior transverse scapular ligament, while the suprascapular nerve passes under the superior transverse scapular ligament (Army goes over the bridge and Navy goes under)
• Veins
  
  • Veins parallel the arteries and share the same names
  • Exception: there is NO thyrocervical vein
  • One artery can have a pair of associated veins
  • Drainage of posterior shoulder is to the transverse cervical vein and suprascapular vein - these drain to the external jugular, which drains to the subclavian