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The arm (brachium) is the region between the shoulder and elbow joints.
Divided by medial and lateral intermuscular septa into:
Anterior compartment (flexor) → musculocutaneous nerve.
Posterior compartment (extensor) → radial nerve.
Anterior compartment muscles: Biceps brachii, Brachialis, Coracobrachialis (BBC).
Posterior compartment muscles: Triceps brachii, Anconeus.
Chief flexor of elbow: Brachialis.
Chief extensor of elbow: Triceps brachii.
Coracobrachialis is pierced by musculocutaneous nerve.
Long head of biceps arises from supraglenoid tubercle, while long head of triceps arises from infraglenoid tubercle — both cross the shoulder joint.
Brachial artery → continuation of axillary artery beyond teres major.
Ends in cubital fossa → divides into radial and ulnar arteries.
Main branches:
Profunda brachii
Superior & inferior ulnar collateral arteries
Muscular branches
Nutrient artery to humerus
Profunda brachii artery → accompanies radial nerve in spiral groove.
Cephalic vein → lateral side → drains into axillary vein.
Basilic vein → medial side → joins brachial veins to form axillary vein.
Median cubital vein → connects cephalic and basilic veins → site for venipuncture.
Bicipital aponeurosis separates brachial artery from median cubital vein.
Musculocutaneous nerve → pierces coracobrachialis → supplies all flexor muscles.
Median nerve → no branches in arm; crosses in front of brachial artery.
Ulnar nerve → passes behind medial epicondyle (funny bone).
Radial nerve → passes in spiral groove with profunda brachii artery → supplies extensors.
Axillary nerve → supplies deltoid and teres minor (near shoulder).
Triangular depression in front of elbow.
Boundaries:
Medial – Pronator teres
Lateral – Brachioradialis
Base – Line joining epicondyles
Contents (medial to lateral): Median nerve, Brachial artery, Biceps tendon, Radial nerve.
Median cubital vein lies superficial to it → used for IV access.
Biceps jerk → C5–C6 → musculocutaneous nerve.
Triceps jerk → C7–C8 → radial nerve.
Brachial pulse: felt medial to biceps tendon in cubital fossa.
Fracture of mid-shaft humerus: injures radial nerve → wrist drop.
Fracture of surgical neck: injures axillary nerve → deltoid paralysis.
Ulnar nerve at medial epicondyle: exposed and painful when struck (“funny bone”).
Volkmann’s ischemic contracture: results from brachial artery injury in supracondylar fractures.
Bicipital tendinitis: inflammation of long head tendon → anterior shoulder pain.
Biceps rupture: produces “Popeye deformity.”
Cubital fossa: site for venipuncture and blood pressure measurement.
Maintained by:
Above elbow: Profunda brachii (radial & middle collateral), superior & inferior ulnar collaterals.
Below elbow: Radial, ulnar, and interosseous recurrent arteries.
Problem:
A 35-year-old male sustains a spiral fracture of the humerus. After injury, he cannot extend his wrist and fingers.
Anatomical Basis:
Radial nerve injury in the spiral groove of humerus → paralysis of wrist and finger extensors.
Triceps partly spared (long and lateral heads intact).
Result: Wrist drop.
Key Sign: Sensory loss over dorsum of hand and posterior forearm.
Problem:
A patient complains of loss of sensation over the lateral side of the forearm following trauma to the arm.
Anatomical Basis:
Musculocutaneous nerve injury (or its continuation, lateral cutaneous nerve of forearm).
May be compressed by fibrosis of coracobrachialis, which the nerve pierces.
Result: Weak flexion at elbow and loss of sensation on lateral forearm.
Problem:
Following fracture of medial epicondyle of humerus, patient presents with clawing of 4th and 5th fingers.
Anatomical Basis:
Ulnar nerve injury behind medial epicondyle.
Paralysis of lumbricals to 4th and 5th fingers → hyperextension at MCP joints, flexion at IP joints.
Sensory loss: medial 1½ fingers (both palmar and dorsal).
Problem:
A knife wound in upper arm causes loss of elbow flexion and weak supination.
Anatomical Basis:
Damage to musculocutaneous nerve → paralysis of biceps brachii and brachialis.
Elbow flexion mainly lost; supination weakened (biceps is chief supinator when flexed).
Problem:
A 40-year-old presents with pain, tingling in thumb, index, and middle fingers after arm trauma.
Anatomical Basis:
Median nerve compression by fibrous bands near insertion of coracobrachialis or between pronator teres heads.
Produces early median nerve entrapment symptoms.
Problem:
A child develops severe flexion deformity of fingers after a supracondylar fracture of humerus.
Anatomical Basis:
Brachial artery injury or spasm → ischemia of forearm flexor muscles.
Results in fibrosis and contracture → claw-like hand.
Early sign: pain on passive finger extension.
Problem:
Loss of biceps reflex following cervical root injury.
Anatomical Basis:
Reflex arc involves musculocutaneous nerve (C5–C6).
Damage to these segments or nerve → absent reflex and weak flexion.
Problem:
A patient reports tenderness over posterior elbow and difficulty extending forearm.
Anatomical Basis:
Injury or strain of triceps tendon insertion on olecranon process.
May also involve anconeus or olecranon bursitis.
Problem:
After supracondylar humeral fracture, brachial pulse absent in cubital fossa.
Anatomical Basis:
Brachial artery trapped or torn by bone fragments.
May cause distal ischemia and Volkmann’s contracture if not treated.
Problem:
After prolonged use of crutches, patient develops sensory loss over posterior arm and wrist drop.
Anatomical Basis:
Radial nerve compression in axilla (Crutch Palsy) → paralysis of triceps, wrist and finger extensors.
Result: Complete wrist drop + sensory deficit posteriorly.
Q1. What are the compartments of the arm and their nerve supply?
→ The arm has two compartments:
Anterior (flexor) → Musculocutaneous nerve
Posterior (extensor) → Radial nerve
Q2. Name the muscles of the anterior compartment of the arm.
→ Biceps brachii, Brachialis, Coracobrachialis.
Q3. Which muscles are supplied by the musculocutaneous nerve?
→ Biceps brachii, Brachialis, Coracobrachialis.
Q4. What are the boundaries and contents of the cubital fossa?
→
Boundaries:
Medial → Pronator teres
Lateral → Brachioradialis
Base → Line joining epicondyles
Contents (medial to lateral): Median nerve, Brachial artery, Biceps tendon, Radial nerve.
Q5. Which structures lie superficial to the cubital fossa?
→ Skin, superficial fascia, median cubital vein, medial and lateral cutaneous nerves of forearm, bicipital aponeurosis.
Q6. What is the chief flexor of the elbow joint?
→ Brachialis.
Q7. What is the chief extensor of the elbow joint?
→ Triceps brachii.
Q8. From where does the long head of biceps arise?
→ Supraglenoid tubercle of scapula.
Q9. What is the nerve supply and root value of triceps?
→ Radial nerve (C6, C7, C8).
Q10. What is the action of coracobrachialis?
→ Flexion and adduction of arm at shoulder joint.
Q11. Which muscle is pierced by musculocutaneous nerve?
→ Coracobrachialis.
Q12. Which muscle is called “the workhorse of elbow flexion”?
→ Brachialis – acts in all positions of forearm.
Q13. Which nerve lies in the spiral (radial) groove of humerus?
→ Radial nerve.
Q14. Which artery accompanies the radial nerve in the spiral groove?
→ Profunda brachii artery.
Q15. What are the branches of the radial nerve in the arm?
→ Muscular (to triceps, anconeus), cutaneous (posterior arm & forearm), articular (elbow joint).
Q16. Which nerve passes behind the medial epicondyle of humerus?
→ Ulnar nerve.
Q17. What is “funny bone” sensation?
→ Tingling/pain due to compression of ulnar nerve behind the medial epicondyle.
Q18. Which nerve lies medial to the brachial artery in the lower arm?
→ Median nerve.
Q19. Which nerve supplies all the flexors of the arm?
→ Musculocutaneous nerve.
Q20. What are the branches of the musculocutaneous nerve?
→ Muscular branches to biceps, brachialis, coracobrachialis, and continuation as lateral cutaneous nerve of forearm.
Q21. What is the main artery of the arm?
→ Brachial artery.
Q22. Where does the brachial artery begin and end?
→ Begins at lower border of teres major → ends in cubital fossa by dividing into radial and ulnar arteries.
Q23. What is the largest branch of brachial artery?
→ Profunda brachii artery (deep artery of arm).
Q24. Which artery supplies the posterior compartment of arm?
→ Profunda brachii artery.
Q25. Which vein connects cephalic and basilic veins?
→ Median cubital vein.
Q26. Why is median cubital vein preferred for venipuncture?
→ Superficial, large, fixed by perforators, and separated from artery by bicipital aponeurosis.
Q27. What is the cause of wrist drop?
→ Radial nerve injury in the spiral groove of humerus.
Q28. What is the cause of Volkmann’s ischemic contracture?
→ Brachial artery obstruction following supracondylar fracture of humerus.
Q29. What is the result of musculocutaneous nerve injury?
→ Weak flexion of elbow and loss of sensation over lateral forearm.
Q30. What is the result of ulnar nerve injury at the elbow?
→ Claw hand deformity (4th and 5th fingers flexed).
Q31. Which nerve injury causes loss of pronation?
→ Median nerve injury.
Q32. What is the significance of the spiral groove?
→ Lodges radial nerve and profunda brachii artery; fracture here causes wrist drop.
Q33. How can the brachial pulse be felt?
→ In cubital fossa, medial to tendon of biceps brachii.
Q34. Which spinal segments are tested by the biceps and triceps jerks?
→
Biceps jerk → C5–C6 (musculocutaneous).
Triceps jerk → C7–C8 (radial).
Q35. What is the main function of the long head of triceps besides extension?
→ Stabilizes and adducts shoulder joint.
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