Locomotor System: Scapular Region

• Faculty of Medicine at Helwan National University presents study material for the academic year 2024-2025.
• This is for Year 1, Semester 2, Module: Locomotor System (Ics) 105.
• The topic is the Scapular Region, presented by Manal Albadawi, Professor Doctor, from the Anatomy & Embryology Department.

Objectives

• Identify the muscles in the scapular region
• Discuss the scapular region muscles, including their origin, insertion, nerve supply, and action
• Describe the arterial anastomosis around the shoulder joint

The Scapula

• It forms a broad triangle with many surface markings, which act as sites for muscle, tendon, and ligament attachment.
• Three borders are the superior, medial (vertebral), and lateral (axillary).
• Muscles positioning the scapula attach along these borders.
• Corners or angles are the superior, inferior, and lateral
• The lateral angle 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 the clavicle, acromion, and spine of the scapula.
• Inserts on the deltoid tuberosity of the humerus.
• The axillary nerve provides nerve supply.
• Anterior fibers cause flexion of the shoulder joint
• Middle fibers cause abduction (15-90 degrees)
• Posterior fibers cause extension of the shoulder joint.
• A subdeltoid/subacromial bursa is present, which is a closed sac lined with synovium and containing fluid, typically in areas subject to friction

Supraspinatus

• Originates from the medial 2/3 of the supraspinous fossa of the scapula
• Inserts on the greater tuberosity of the humerus and the capsule of the shoulder joint.
• The suprascapular nerve (C5, 6) provides nerve supply.
• Abducts the arm and stabilizes the shoulder joint
• Initiates abduction from 0-15 degrees.

Infraspinatus

• Originates from the medial 2/3 of the infraspinous fossa of the scapula.
• Inserts on the greater tuberosity of the humerus and the capsule of the shoulder joint.
• The suprascapular nerve (C5, 6) provides nerve supply.
• Laterally rotates the arm and stabilizes the shoulder joint.

Teres Minor

• Originates from the upper two-thirds of the lateral border of the scapula.
• Inserts on the greater tuberosity of the humerus and capsule of the shoulder joint.
• Receives nerve supply from the axillary nerve (C5, 6).
• Laterally rotates the arm and stabilizes the shoulder joint

Teres Major

• Originates from the lower third of the lateral border of the scapula.
• Inserts on the medial lip of the bicipital groove of the humerus.
• The lower subscapular nerve (C6, 7) provides nerve supply.
• Medially rotates and adducts the arm, while also stabilizing the shoulder joint.

Subscapularis

• Originates from the medial 2/3 of the subscapular fossa.
• Insertion is on the lesser tubercle of the humerus.
• Receives nerve supply from the upper and lower subscapular nerves (C5, 6, 7).
• Action includes medially rotating the arm and stabilizing the shoulder joint

Rotator Cuff Muscles

• Supraspinatus
• Infraspinatus
• Teres Minor
• Subscapularis
• These muscles reinforce the capsule of the shoulder joint, providing active support during movements and pulling the head of the humerus medially towards the glenoid cavity

Intermuscular Spaces

• Quadrangular Space
• Bounded superiorly by the teres minor, inferiorly by the teres major, medially by the long head of the triceps brachii, and laterally by the surgical neck of the humerus
• Transmits the axillary nerve and the posterior circumflex humeral artery.
• Medial Triangular Space
• Bounded by the teres minor superiorly, the teres major inferiorly, and the long head of the triceps laterally.
• Contains the circumflex scapular vessels.
• Lateral Triangular Space
• Bounded by the teres major superiorly, the long head of the triceps medially, and the humerus laterally.
• Contains the radial nerve and profunda brachii artery.

Arterial Anastomosis Around the Shoulder Joint

• The shoulder’s extreme mobility can kink the axillary artery, causing temporary occlusion
• Compensation achieved via arterial anastomosis between branches of the subclavian and axillary arteries
• This ensures adequate blood flow to the upper limb regardless of arm position.

Rotator Cuff Tendinitis

• Manifestations: Spasm and pain in the middle range of abduction, common cause of pain in shoulder region
• Cause: Excessive overhead activity which causes degenerative changes in the subacromial bursa. This is followed by degenerative changes in the supraspinatus tendon and extends to the other tendons of the rotator cuff.

Clinical Applications

• Fractures of the Scapula
• Usually result from severe trauma
• Often associated with fractured ribs
• Muscles on the anterior and posterior surfaces adequately splint the fragments.
• Dropped Shoulder
• Occurs with paralysis of the trapezius muscle.
• Winged Scapula
• Caused by paralysis of the serratus anterior
• The medial border and 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

• Six muscles converge from the scapula to the humerus: deltoid, supraspinatus, infraspinatus, teres minor, teres major, and subscapularis
• Three of these (supraspinatus, infraspinatus, teres minor) extend from the posterior surface of the scapula to insert on the greater tubercle of the humerus
• Subscapularis passes from the thoracic surface of the scapula to the lesser tubercle.