Shoulder, Scapular Region and Back

Upper Limb Lecture 1: Shoulder, Posterior Scapular Region and Back

• The lecture focuses on components of the shoulder and posterior scapular region, including muscles, origins, insertions, neurovasculature, actions, and posterior scapular gateways.

Pectoral Girdle Overview

• Associated with the lateral aspect of the lower portion of the neck and thoracic wall.
• It is suspended by the clavicle joint with the sternum and numerous muscles
• It has a large range of motion and connects to the thoracic wall
• Communicates with the back and pectoral region
• Regions include the shoulder, arm, forearm, wrist, and hand
• Transitional areas include the axilla, cubital fossa, and carpal tunnel
• The function is to position the hand in space. Its mechanical tool- enables grip and manipulation. Its sensory tool for discrimination through palmar pads rich in receptors

Bones

• The bones of the shoulder include the clavicle, scapula, and humerus

Clavicle

• The only bony attachment between the trunk and upper limb
• It extends between the manubrium of the sternum and the acromion of the scapula
• It has a slender 'S' shape
• The medial aspect is convex, and the lateral aspect is concave
• It is palpable through its entire length
• The medial end has a quadrangular sternal end
• The lateral end has a flattened acromial end
• The inferior surface of the lateral third is rougher than the superior surface, featuring the subclavian groove, conoid tubercle, and trapezoid line

Scapula

• Triangular with 3 angles: lateral, medial, and inferior
• The lateral angle features the glenoid cavity
• There are 3 borders: superior, medial (thin and sharp), and lateral (thickened attachments)
• Superior border features the coracoid process and suprascapular notch
• The processes include the spinous, acromion, and coracoid
• There are 2 surfaces: costal, with the subscapular fossa, and posterior, divided by the spine into smaller supraspinous fossa and larger infraspinous fossa.

Shoulder Muscles

• The superficial muscles attach to opposing surfaces of the scapula, acromion, and clavicle
• Bony landmarks are palpable between the trapezius and deltoid

Trapezius

• Attaches the scapula to the trunk
• Origin extends from CI to TXII, with CI to CVII via ligamentum nuchae
• Insertion is a U-shaped attachment in a horizontal plane
• Innervated by the accessory nerve (CN IX) and anterior rami of C3 and C4
• Action is a powerful elevator; tested by shrugging the shoulder against resistance

Deltoid

• Muscle that’s attached to the scapula and clavicle to the humerus
• Originates from a U-shaped attachment in the horizontal plane
• Inserts on the deltoid tuberosity of the humerus
• Abducts the arm after the first 15 degrees; clavicular fibers aid flexion & posterior fibers aid extension

Deep Muscles: Levator Scapulae, Rhomboid Minor, and Rhomboid Major

• Elevates the scapula
• Elevate and retract scapula
• All innervated by the dorsal scapular nerve

Posterior Scapular Region

• Deep to the trapezius and deltoid and includes 4 muscles

Posterior Scapular Muscles

• Supraspinatus
• Infraspinatus
• Teres minor
• Teres major
• Long head of triceps originates outside the scapula on the olecranon

Rotator Cuff Muscles (SITS)

• Supraspinatus
• Infraspinatus
• Teres minor
• Subscapularis

Rotator Cuff Function

• Tendons blend with the joint capsule
• These muscles provide strong lateral stability and stabilize the head of the humerus in the glenoid cavity, preventing dislocation.

Posterior Scapular Gateways

• Suprascapular foramen
• Quadrangular space
• Upper triangular space
• Lower triangular Space

Suprascapular Foramen

• Provides route between base of the neck and posterior scapular region
• Boundaries: Suprascapular notch of scapula (Inf) and Suprascapular ligament (Sup)
• Transmits the suprascapular nerve
• Vessels usually follow the nerve above the ligament

Quadrangular Space

• Route between anterior regions like axilla and posterior scapular region
• Boundaries include the inferior margin of teres minor, surgical neck of humerus, superior margin of teres major, and lateral margin of long head of triceps brachii
• It transmits the axillary nerve and posterior circumflex humeral artery

Upper Triangular Space

• Route between anterior and posterior arm and axilla
• Boundaries: Medial margin of long head of triceps brachii, inferior margin of teres minor, and superior margin of teres major
• Transmits the circumflex scapular artery and vein

Lower Triangular Space

• Route between axilla and posterior scapular region
• Boundaries include the lateral margin of long head of triceps, shaft of the humerus, and inferior margin of teres major
• Transmits the radial nerve, may be injured by a fracture of the surgical neck of the humerus, and profunda brachii artery and associated veins

Arterial Anastomosis

• The medial border of scapula receives blood from the subclavian artery via the thyrocervical trunk (transverse cervical artery → deep branch)
• Superior border from the subclavian artery via the thyrocervical trunk (suprascapular artery)
• Lateral border from axillary artery (subscapular artery → circumflex scapular artery)
• Head and neck of the humerus from the axillary artery (anterior and posterior circumflex humeral arteries)

Back Muscles

• The extrinsic (appendicular group) back muscles originate embryonically from a location other than the back
• There are superficial and intermediate muscles
• Innervated by anterior rami of spinal nerves
• Functions – produce and control movements
• Intrinsic (deep) back muscles: Develop in the back and innervated by posterior rami of spinal nerves and functions to maintain posture and move the vertebral column

Superficial Extrinsic Muscles

• Trapezius
• Latissimus dorsi

Deeper Extrinsic Muscles

• Levator scapulae
• Rhomboid minor
• Rhomboid major

Intermediate Extrinsic Muscles

• Positioning of muscles suggests that they have a respiratory function
• Serratus posterior superior elevates ribs, innervated by segmental branches of anterior rami of upper thoracic nerves T2-T5.
• Serratus posterior inferior depresses ribs, innervated by segmental branches of anterior rami of lower thoracic nerves T9-T12.