Pectoral Region & Axilla Practice Flashcards

Osteology of the Pectoral Girdle

• General Composition: The upper limb is suspended from the thorax by the pectoral girdle. It consists of two primary bones:

  • Clavicle: Articulates medially with the sternum and laterally with the scapula.

  • Scapula: Articulates medially with the clavicle and laterally with the humerus.

• Clavicle Anatomy:

  • Sternal end: The medial end, characterized by a rounded shape.

  • Acromial end: The lateral end, characterized by a flat shape.

  • Shaft: The body of the bone.

  • Subclavian groove: Located on the inferior surface; serves for muscle attachment.

  • Trapezoid line: Found on the inferior-lateral aspect.

  • Conoid tubercle: Found on the inferior-lateral aspect, medial to the trapezoid line.

  • Impression for costoclavicular ligament: Located on the inferior-medial aspect.

  • Orientation of the Clavicle:

    1. Medial vs. Lateral: Medial end is round; lateral end is flat.

    2. Superior vs. Inferior: Superior surface is smooth; inferior surface contains the subclavian groove.

    3. Convexity/Concavity: Medial $\frac{1}{2}$ is convex anteriorly; lateral $\frac{1}{2}$ is concave anteriorly.

• Fracture of the Clavicle:

  • Etiology: Most commonly caused by a fall onto the lateral shoulder; less commonly by a direct blow to the bone.

  • Pathophysiology: Most frequent in the middle third segment.

  • Clinical Features:

    1. Shortening of the clavicle.

    2. Drooping of the affected shoulder.

    3. Bulging of the skin at the fracture site (evident on PA view X-ray).

• Scapula Anatomy:

  • Borders: Medial border, Lateral border, and Superior border.

  • Angles: Inferior angle and Superior angle.

  • Cavities and Fossae:

    • Glenoid cavity: Articulates with the humerus.

    • Supraspinous fossa: Depressed area superior to the spine (posterior).

    • Infraspinous fossa: Depressed area inferior to the spine (posterior).

    • Subscapular fossa: Large concave area on the anterior surface.

  • Processes and Notches:

    • Acromion process: Lateral extension of the spine.

    • Coracoid process: Hook-like projection on the anterior-superior aspect.

    • Spine: Prominent ridge on the posterior surface.

    • Suprascapular notch: Located on the superior border.

• Sternum Anatomy:

  • Parts: Manubrium, Body, and Xiphoid process.

  • Notches:

    • Jugular notch: Superior indentation on the manubrium.

    • Clavicular notch: Articulation point for the sternal end of the clavicle.

Sternoclavicular & Acromioclavicular Joints

• Sternoclavicular (SC) Joint:

  • Type: Saddle-type synovial joint.

  • Ligaments:

    • Sternoclavicular ligament (Anterior and Posterior).

    • Interclavicular ligament (Connects the two clavicles).

    • Costoclavicular ligament (Anchors clavicle to the $1^{st}$ rib).

  • Components: Includes an articular disc.

  • Movements:

    • Protraction/Retraction (Posterior/Anterior glide).

    • Elevation/Depression (Inferior/Superior glide).

    • Axial rotation.

• Acromioclavicular (AC) Joint:

  • Type: Plane-type synovial joint.

  • Ligaments:

    • Acromioclavicular ligament.

    • Coracoclavicular (CC) ligament: Composed of the Trapezoid ligament (lateral) and Conoid ligament (medial).

    • Coracoacromial ligament: Connects the coracoid process to the acromion.

  • Movements: Rotation of the clavicle about its longitudinal axis.

• Shoulder (AC Joint) Separation:

  • Etiology: Most commonly a direct blow to the superior aspect of the acromion; less commonly falling onto an outstretched hand (FOOSH).

  • Pathophysiology:

    • Mild: Isolated tear of the joint capsule and acromioclavicular ligament.

    • Severe: Combined tear of the acromioclavicular and coracoclavicular ligaments.

  • Clinical Features: Prominent lateral end of the clavicle (bulging superiorly) and a prominent acromion.

Blood Vessels of the Pectoral Region and Axilla

• Main Arteries:

  • Subclavian Artery: Becomes the axillary artery at the lateral border of the $1^{st}$ rib.

  • Axillary Artery: Divided into three parts by the Pectoralis minor muscle.

    • Part 1 (Medial to Pectoralis minor): 1 branch.

      1. Superior thoracic artery: Supplies subclavius and muscles/skin of the $1^{st}$ and $2^{nd}$ intercostal spaces.

    • Part 2 (Posterior to Pectoralis minor): 2 branches.

      1. Thoracoacromial artery: Has 4 branches (Pectoral, Clavicular, Acromial, Deltoid). Supplies Pectoralis major/minor, subclavius, AC joint, and deltoid.

      2. Lateral thoracic artery: Supplies Serratus anterior.

    • Part 3 (Lateral to Pectoralis minor): 3 branches.

      1. Subscapular artery: Largest branch; divides into Circumflex scapular artery (Infraspinatus, Teres minor) and Thoracodorsal artery (Latissimus dorsi, Teres major).

      2. Anterior circumflex humeral artery: Wraps around the surgical neck of the humerus.

      3. Posterior circumflex humeral artery: Wraps around the surgical neck; supplies Teres minor.

  • Brachial Artery: Continuation of the axillary artery at the inferior border of the Teres major muscle.

  • Mnemonic for Axillary Branches: Send The Lord So A Prayer (Superior thoracic, Thoracoacromial, Lateral thoracic, Subscapular, Anterior circumflex humeral, Posterior circumflex humeral).

• Venous Drainage:

  • Deep Veins: Brachial vein, Axillary vein, Subclavian vein.

  • Superficial Veins:

    • Cephalic vein: Drains the lateral aspect of the upper limb.

    • Basilic vein: Drains the medial aspect.

    • Median cubital vein: Located anterior to the elbow; joins cephalic and basilic veins. Primary site for IV access and venipuncture.

Nerves – Brachial Plexus

• Structural Organization: Roots ($C5$, $C6$, $C7$, $C8$, $T1$) $→$ Trunks (Superior, Middle, Inferior) $→$ Divisions (Anterior, Posterior) $→$ Cords (Lateral, Posterior, Medial) $→$ Terminal Branches.

  • Mnemonic: Remember To Drink Cold Beer!

• Accessory Branches (Roots/Trunks):

  • Dorsal scapular nerve ($C5$): Rhomboids, Levator scapulae.

  • Long thoracic nerve ($C5$-$C7$): Serratus anterior.

  • Suprascapular nerve ($C5$, $C6$): Supraspinatus, Infraspinatus.

  • Nerve to subclavius ($C5$, $C6$): Subclavius muscle.

• Accessory Branches (Cords):

  • Lateral Pectoral nerve ($C5$-$C7$): Pectoralis major.

  • Medial Pectoral nerve ($C8$, $T1$): Pectoralis major and minor.

  • Upper Subscapular nerve ($C5$, $C6$): Subscapularis.

  • Thoracodorsal nerve ($C6$-$C8$): Latissimus dorsi.

  • Lower Subscapular nerve ($C5$, $C6$): Subscapularis, Teres major.

  • Medial brachial cutaneous ($C8$, $T1$): Sensory to medial distal arm.

  • Medial antebrachial cutaneous ($C8$, $T1$): Sensory to medial forearm.

• Terminal Branches:

  • Musculocutaneous ($C5$-$C7$): Biceps brachii, brachialis, coracobrachialis. Sensory to lateral forearm.

  • Median ($C5$-$T1$): Hand/wrist flexors (mostly), thenar muscles. Sensory to lateral palmar hand.

  • Ulnar ($C8$, $T1$): Two forearm flexors, most intrinsic hand muscles. Sensory to medial hand.

  • Axillary ($C5$, $C6$): Deltoid, Teres minor. Sensory to lateral upper arm.

  • Radial ($C5$-$T1$): Arm/forearm extensors. Sensory to posterior arm/forearm and dorsolateral hand.

  • Mnemonic: 3 Musketeers Assassinated 5 Rats, 5 Mice and 2 Unicorns ($C5$-$C7$ Musculocutaneous, $C5$-$C6$ Axillary, $C5$-$T1$ Radial, $C5$-$T1$ Median, $C8$-$T1$ Ulnar).

Muscles of the Pectoral Region and Axilla

• Pectoral Region Muscles:

  • Pectoralis Major:

    • Origin: Anterior sternum/clavicle, costal cartilages 1-6.

    • Insertion: Lateral lip of intertubercular sulcus of humerus.

    • Action: Adducts/internally rotates shoulder. Clavicular head flexes shoulder; Sternocostal head extends shoulder from flexed position.

    • Innervation: Lateral ($C5$-$C7$) and Medial ($C8$, $T1$) pectoral nerves.

  • Pectoralis Minor:

    • Origin: Ribs 3-5.

    • Insertion: Coracoid process.

    • Action: Stabilizes scapula (draws it anteriorly/inferiorly).

    • Innervation: Medial pectoral nerve ($C8$, $T1$).

  • Serratus Anterior:

    • Origin: Ribs 1-8/9.

    • Insertion: Anterior surface of medial border of scapula.

    • Action: Protracts/stabilizes scapula; upward rotation for shoulder abduction.

    • Innervation: Long thoracic nerve ($C5$-$C7$).

  • Subclavius:

    • Origin: $1^{st}$ rib. Insertion: Inferior clavicle.

    • Action: Depresses clavicle. Innervation: Nerve to subclavius ($C5$, $C6$).

• Axilla Boundaries and Contents:

  • Apex: Superior opening; Base: Skin/tissue.

  • Anterior Wall: Pectoralis major and minor.

  • Medial Wall: Thoracic wall and Serratus anterior.

  • Posterior Wall: Subscapularis, Teres major, Latissimus dorsi.

  • Lateral Wall: Intertubercular sulcus of the humerus.

  • Contents: Axillary artery, Axillary vein, Brachial plexus (cords/branches), Axillary lymph nodes.

Brachial Plexus Lesions

• Erb Palsy ("Waiter's Tip"):

  • Pathophysiology: Injury to superior trunk ($C5$, $C6$).

  • Etiology: Lateral traction on neck during birth; falling on head/shoulder.

  • Muscles/Nerves Affected: Suprascapular, Axillary, Musculocutaneous. Weakness in abduction, external rotation, elbow flexion, and supination.

  • Posture: Shoulder adducted/internally rotated; elbow extended; wrist flexed; hand pronated.

  • Features: Sensory loss (lateral arm/forearm/thumb); absent Moro and Biceps reflexes.

• Klumpke Palsy ("Claw Hand"):

  • Pathophysiology: Injury to inferior trunk ($C8$, $T1$).

  • Etiology: Hyperabduction of arm (FOOSH, birth injury); Pancoast tumor compression.

  • Muscles Affected: Intrinsic hand muscles (thenar, hypothenar, lumbricals, interossei).

  • Features: "Total claw" (MCP hyperextended, IP flexed); Horner's Syndrome (Ptosis, Miosis, Anhidrosis); sensory loss (medial forearm/hand).

• Saturday Night/Crutch Palsy ("Wrist Drop"):

  • Pathophysiology: Injury to radial nerve in the axilla.

  • Etiology: Compression (sleeping with arm over chair, crutches).

  • Clinical Features: Wrist drop (impaired extension of wrist/digits); weakness in triceps (impaired elbow extension); absent triceps reflex; sensory loss on dorsal-lateral 3.5 digits.

• Long Thoracic Nerve Lesion ("Winged Scapula"):

  • Pathophysiology: Injury to Long thoracic nerve ($C5$-$C7$); paralysis of Serratus anterior.

  • Etiology: Stab wound to axilla; axillary surgery.

  • Clinical Features: Protrusion of medial border of scapula; inability to abduct arm past $90^{\circ}$.

Lymphatics of the Chest, Breast, and Axilla

• Local Lymph Nodes:

  • Subareolar lymphatic plexus, Interpectoral, Parasternal, Supraclavicular, Infraclavicular.

  • Axillary Nodes: Humeral (Lateral), Pectoral (Anterior), Subscapular (Posterior), Central, and Apical.

• Clinical Application:

  • Drainage patterns assist in breast cancer staging and prognosis.

  • Sentinel lymph node biopsy: Identifies the first node(s) receiving drainage from a tumor.

  • Benign vs. Malignant Nodes:         | Feature | Malignant | Benign |         | :--- | :--- | :--- |         | Size | Larger (Over $2\,cm$) | Smaller (Under $2\,cm$) |         | Consistency | Hard, firm, or rubbery | Soft |         | Mobility | Fixed | Mobile |         | Tenderness | Usually non-tender | Usually tender |         | Duration | Chronic (Over $2\,weeks$) | Acute (Under $2\,weeks$) |

Practice Questions Summary

• Bone ID: Identification of scapular landmarks (Acromion, Spine, Infraspinous/Supraspinous/Subscapular fossae, etc.).

• AC Joint: A prominent bulge on the lateral shoulder post-tackle implies damage to the Acromioclavicular ligament.

• Arterial Divisions: The Circumflex scapular artery emerges from the $3^{rd}$ division (via the subscapular artery).

• Radial Roots: The Posterior cord (and Radial nerve) contains fibers from $C5$-$T1$.

• Muscle Action: Serratus anterior is responsible for scapula protraction.

• Clinical Scenario: A patient unable to grasp items with medial forearm numbness after a fall (hyperabduction) likely presents with Klumpke Palsy, characterized by hyperextension at the MCP joints.