Locomotor System: Scapular Region Muscles

• Helwan National University, Faculty of Medicine
• Academic year is 2024-2025
• Year 1, semester 2
• Module: Locomotor system (Ics) 105
• Scapular region study notes by Dr. Manal Albadawi (Professor Doctor), Department of Anatomy & Embryology

Objectives

• Identify the scapular region muscles
• Discuss scapular region muscles (origin, insertion, nerve supply, and action)
• Learn about arterial anastomosis around the shoulder joint

Scapula

• The scapula body is a broad triangle with many surface markings
• These markings serve as attachment sites for muscles, tendons, and ligaments
• The three borders of the scapular triangle are superior, medial (vertebral), and lateral (axillary)
• Muscles that position the scapula attach along these edges
• The corners/angles of the scapula are superior, inferior, and lateral
• The lateral angle, or scapula head, forms a broad process that supports the glenoid cavity (fossa)

Muscles of the Shoulder Girdle

• Deltoid
• Supraspinatus
• Infraspinatus
• Teres Minor
• Teres Major
• Subscapularis

Deltoid Muscle

• Originates from the lateral third of clavicle, acromion, and spine of the scapula
• Inserts on the deltoid tuberosity of humerus
• Nerve supply: Axillary nerve
• Anterior fibers: flexion of the shoulder joint
• Middle fibers: abduction (15-90 degrees)
• Posterior fibers: extension of the shoulder joint
• Subdeltoid/subacromial bursa is a closed sac lined with synovium and fluid filled, found in areas subject to friction

Supraspinatus

• Origin: medial 2/3 of supraspinous fossa of scapula
• Insertion: greater tuberosity of humerus, capsule of shoulder joint
• Nerve supply: suprascapular nerve C5, 6
• Action: abducts arm, stabilizes shoulder joint, and initiates abduction (0-15 degrees)

Infraspinatus

• Origin: Medial 2/3 infraspinous fossa of scapula
• Insertion: Greater tuberosity of humerus, capsule of shoulder joint
• Nerve Supply: Suprascapular nerve C5, 6
• Action: Laterally rotates arm and stabilizes shoulder joint

Teres Minor

• Origin: Upper two thirds of lateral border of scapula
• Insertion: Greater tuberosity of humerus, capsule of the shoulder joint
• Nerve Supply: Axillary nerve C5, 6
• Action: Laterally rotates arm and stabilizes shoulder joint

Teres Major

• Origin: Lower third of lateral border of scapula
• Insertion: Medial lip of bicipital groove of humerus
• Nerve supply: Lower subscapular nerve C6, 7
• Action: Medially rotates and adducts the arm and stabilizes the shoulder joint

Subscapularis

• Origin: Medial 2/3 subscapular fossa
• Insertion: Lesser tubercle of humerus
• Nerve Supply: Upper and lower subscapular nerves C5, 6, 7
• Action: Medially rotates arm and stabilizes shoulder joint

Rotator Cuff Muscles

• Supraspinatus
• Infraspinatus
• Teres Minor
• Subscapularis
• These muscles reinforce the capsule of the shoulder joint and provide active support during movement
• This is achieved by pulling the head of the humerus medially towards the glenoid cavity

Intermuscular Spaces

• Quadrangular Space:
  • Superior border: Teres minor
  • Inferior border: Teres major
  • Medial border: Long head of the Triceps brachii
  • Lateral border: Surgical neck of the humerus
  • Contents: Axillary nerve and posterior circumflex humeral artery
• Medial Triangular Space:
  • Superior border: Teres minor
  • Inferior border: Teres major
  • Lateral border: Long head of the Triceps
  • Contents: circumflex scapular vessels
• Lateral Triangular Space:
  • Superior border: Teres major
  • Medial border: Long head of the Triceps
  • Lateral border: Humerus
  • Contents: Radial nerve and profunda brachii artery

Arterial Anastomosis around the shoulder joint

• Extreme mobility may result in kinking of the axillary artery, causing temporary occlusion
• An important arterial anastomosis compensates for this
• Anastomosis exists between branches of the subclavian and axillary arteries, ensuring adequate blood flow, regardless of arm position

Rotator Cuff Tendinitis

• Manifestations: Spasm associated with pain in the middle range of abduction is a common cause of shoulder pain
• Cause: Excessive overhead activity can cause degenerative changes in the subacromial bursa.
• Degenerative changes in the supraspinatus tendon can extend to the other rotator cuff tendons.

Clinical Applications

• Fractures of the Scapula:
  • Result of severe trauma (e.g., run-over accidents, car crashes)
  • Often associated with fractured ribs
  • Muscles on the anterior and posterior surfaces adequately splint the fragments
• Dropped Shoulder:
  • Occurs with paralysis of the trapezius
• Winged Scapula:
  • Caused by paralysis of the Serratus anterior due to damage to the Long thoracic nerve
  • The medial border, and particularly the inferior angle, of the scapula elevate away from the thoracic wall when pushing forward with the arm
  • Normal arm elevation is no longer possible

Summary

• A group of six muscles converge from the scapula to the humerus and surround the shoulder joint
  • These include deltoid, supraspinatus, infraspinatus, teres minor, teres major, and subscapularis
• Supraspinatus, infraspinatus, and teres minor extend from the posterior surface of the scapula
  • Insert into the three impressions on the greater tubercle of the humerus
• Subscapularis passes from the thoracic surface of the scapula to the lesser tubercle.