Arm and Cubital Fossa

Humerus - Arm's Bony Pillar

• Overview: Longest bone, upper limb. Articulates: scapula (glenohumeral joint), radius & ulna (elbow joint).
• Proximal Features:
  • Head, Anatomical Neck, Surgical Neck (⚠️ Axillary nerve injury risk with fracture).
  • Greater & Lesser Tubercles (muscle attachments), Intertubercular Sulcus (bicipital groove).
  • 📌 Mnemonic for intertubercular sulcus tendons: "A lady between two majors" (Pectoralis Major, Latissimus Dorsi, Teres Major).
• Shaft Features:
  • Deltoid Tuberosity (deltoid insertion).
  • Radial (Spiral) Groove (⚠️ Radial nerve & profunda brachii artery injury with mid-shaft fracture).
• Distal Features (Elbow Joint):
  • Medial Epicondyle (⚠️ Ulnar nerve injury risk with fracture), Lateral Epicondyle.
  • Capitulum (articulates with radius), Trochlea (articulates with ulna).
  • Coronoid Fossa, Olecranon Fossa, Radial Fossa.

⭐ Supracondylar fracture of the humerus is common in children and can lead to Volkmann's ischemic contracture due to brachial artery injury and subsequent compartment syndrome.

Arm Muscles - Flex & Extend

Anterior Compartment (Flexors): Innervated by Musculocutaneous nerve (C5, C6, C7).

• Biceps Brachii:
  • Action: Supinates forearm, flexes elbow.
  • Heads: Short (coracoid process), Long (supraglenoid tubercle).
• Coracobrachialis:
  • Action: Flexes & adducts arm.
  • Note: Pierced by musculocutaneous nerve.
• Brachialis:
  • Action: Main flexor of forearm at elbow.

📌 Mnemonic for anterior compartment: BBC (Biceps, Brachialis, Coracobrachialis).

Posterior Compartment (Extensors): Innervated by Radial nerve (C5-T1).

• Triceps Brachii:
  • Action: Main extensor of forearm at elbow.
  • Heads: Long (infraglenoid tubercle), Lateral, Medial.
• Anconeus:
  • Action: Assists triceps in extension, stabilizes elbow.

⭐ Rupture of the long head of the biceps brachii tendon is a common injury, often presenting with a "Popeye sign" (a bulge in the distal arm due to muscle retraction).

Arm's Neurovascular Bundle - Vital Conduits

• Brachial Artery: Main arm supply (from axillary a.).
  • Travels with median n. (nerve lat → crosses ant → med).
  • Branches: Profunda brachii (with radial n.), ulnar collaterals.
  • Terminates: Radial & Ulnar aa. in cubital fossa.
• Nerves:
  • Median: Crosses brachial a.; no arm motor supply. Risk in supracondylar #.
  • Ulnar: Posterior to medial epicondyle; no arm branches.
  • Radial: In radial groove (w/ profunda brachii); supplies triceps. Risk in mid-shaft humeral #.
  • Musculocutaneous: Pierces coracobrachialis; supplies ant. compartment (BBC - Biceps, Brachialis, Coracobrachialis); → lat. cut. n. forearm.
• Veins: Deep (brachial vv.); Superficial (cephalic, basilic, median cubital for venipuncture).

⭐ Cubital fossa contents (medial to lateral): Median N., Brachial A., Biceps Tendon, Radial N. (deep). 📌 M-B-B-R (Median N., Brachial A., Biceps Tendon, Radial N.).

Cubital Fossa - Elbow's Crossroads

• Triangular depression anterior to elbow joint.
• Boundaries:
  • Superior: Imaginary line connecting medial & lateral epicondyles.
  • Medial: Lateral border of Pronator Teres.
  • Lateral: Medial border of Brachioradialis.
  • Floor: Brachialis & Supinator muscles.
  • Roof: Skin, superficial fascia (with median cubital vein), deep fascia, bicipital aponeurosis.
• Contents (Medial to Lateral): 📌 My Blood Turns Red
  • Median Nerve
  • Brachial Artery (bifurcates into radial & ulnar arteries)
  • Biceps Brachii Tendon
  • Radial Nerve (divides into superficial & deep branches)

⭐ The median cubital vein in the roof is a common site for venipuncture. The brachial artery and median nerve are vulnerable in supracondylar fractures of the humerus.

High‑Yield Points - ⚡ Biggest Takeaways

• Musculocutaneous nerve pierces coracobrachialis; supplies anterior arm muscles (BBC: Biceps, Brachialis, Coracobrachialis).
• Radial nerve in spiral groove supplies triceps; vulnerable in humerus mid-shaft fractures.
• Brachial artery is palpable medial to biceps; bifurcates in cubital fossa into radial & ulnar arteries.
• Cubital fossa contents (Medial to Lateral): Median nerve, Brachial Artery, Biceps tendon, Radial nerve (MBBR).
• Median cubital vein, in cubital fossa roof, is prime site for venipuncture.
• Supracondylar humerus fracture commonly injures brachial artery & median nerve.
• Biceps brachii flexes & supinates forearm; brachialis is main elbow flexor; triceps brachii extends elbow_._