Introduction to the Arm Anatomy

Introduction to the Arm

• The arm is the part of the upper limb between the shoulder and the elbow.
• Deep fascia surrounds the arm, creating anterior and posterior compartments.
• Lateral and medial intermuscular septa divide the arm into compartments.
• The ulnar nerve and superior ulnar collateral artery traverse the medial intermuscular septum to enter the posterior arm compartment.
• The radial nerve and radial collateral artery traverse the lateral intermuscular septum to enter the anterior arm compartment.

Anterior Compartment

• The anterior arm compartment contains the following muscles:
  • Coracobrachialis
  • Brachialis
  • Biceps brachii
• The anterior compartment is innervated by the:
  • Musculocutaneous nerve
  • Median nerve
  • Ulnar nerve (upper half, medially)
  • Radial nerve (lower half, laterally)
  • Medial cutaneous nerves of the arm and forearm
• The anterior compartment has the following vessels:
  • Brachial artery
  • Brachial veins

Posterior Compartment

• The posterior compartment contains the following:
  • Triceps brachii muscle
  • Radial nerve and profunda brachii vessels in the spiral groove
  • Ulnar nerve (lower half, medially)

Muscles of the Anterior Compartment

• Coracobrachialis:
  • Origin: apex of the coracoid process
  • Insertion: mid-shaft of humerus (medial side)
  • Innervation: musculocutaneous nerve (C5, C6, C7)
  • Function: flexes the arm at the glenohumeral joint
• Biceps brachii:
  • Origin:
    • Long head: supraglenoid tubercle of scapula
    • Short head: apex of coracoid process
  • Insertion: radial tuberosity
  • Innervation: musculocutaneous nerve (C5, C6)
  • Function:
    • Flexes the forearm at the elbow joint
    • Supinates the forearm
    • Accessory flexor of the arm at the glenohumeral joint
• Brachialis:
  • Origin: anterior aspect of humerus
  • Insertion: tuberosity of the ulna
  • Innervation: musculocutaneous nerve (C5, C6) and a small contribution by the radial nerve (C7)
  • Function: powerful flexor of the forearm at the elbow joint

Muscles of the Posterior Compartment

• Triceps brachii:
  • Origin:
    • Long head: infraglenoid tubercle of scapula
  • Insertion: olecranon
  • Innervation: radial nerve (C6, C7, C8)
  • Function: extends the forearm at the elbow joint

Nerves of the Arm

• Median Nerve:
  • No major branches in the arm
  • Branch to pronator teres muscle may arise proximal to the elbow joint
• Ulnar Nerve:
  • No major branches in the arm
• Radial Nerve:
  • Muscular branches innervate the triceps brachii and the lateral part of the brachialis muscles.
  • Cutaneous branches include:
    • Inferior/Lower lateral cutaneous nerve of arm
    • Posterior cutaneous nerve of forearm

The Elbow Joint

• The elbow joint is a complex joint with three articulations sharing a common synovial cavity:
  • Trochlear notch of the ulna with the trochlea of the humerus
  • Head of the radius with the capitulum of the humerus
• Movements at the elbow joint include flexion and extension of the forearm on the arm.

The Proximal Radio-Ulnar Joint

• The head of the radius articulates with the radial notch of the ulna.
• This joint is responsible for pronation and supination of the forearm.

Elbow Joint Structures

• Articular surfaces are covered with hyaline cartilage.
• Synovial membrane lines the radial fossa, coronoid fossa, olecranon fossa, joint capsule, and medial surface of the trochlea.

Ligaments of the Elbow Joint

• Fibrous membrane of the joint capsule is thickened medially and laterally to form collateral ligaments.
• The anular ligament of the radius reinforces the joint capsule laterally, cupping the head of the radius.
• The anular ligament blends with the radial collateral ligament posteriorly.

The Cubital Fossa

• Triangular intermuscular space located anterior to the elbow.
• Boundaries:
  • Base: line between the medial and lateral epicondyles of the humerus
  • Medial boundary: lateral margin of the pronator teres muscle
  • Lateral boundary: medial margin of the brachioradialis muscle
  • Apex: where the pronator teres and brachioradialis muscles cross
  • Floor: brachialis (upper part) and supinator (lower part)
  • Roof: skin, superficial fascia, deep fascia, bicipital aponeurosis
• Contents from lateral to medial:
  • Tendon of the biceps brachii muscle
  • Brachial artery
  • Median nerve
• Other structures in the cubital fossa:
  • Brachial artery bifurcates into the radial and ulnar arteries at the apex
  • Radial nerve is superficial to the brachioradialis muscle

Radial Artery

• Exits the cubital fossa through the apex and enters the forearm.
• Gives off the radial recurrent artery, contributing to the elbow anastomosis.

Ulnar Artery

• Exits the cubital fossa deep to the ulnar head of the pronator teres.
• Branches in the cubital fossa:
  • Anterior and posterior ulnar recurrent arteries
  • Common interosseous artery (divides into anterior and posterior interosseous arteries)
  • Interosseous recurrent branch (arises from the posterior interosseous artery and contributes to the elbow anastomosis)

Elbow Anastomosis

• Arterial anastomosis around the elbow
• Medial Anastomosis:
  • Anterior:
    • Anterior branch of the inferior ulnar collateral artery (from the brachial artery)
    • Anterior ulnar recurrent artery (from the ulnar artery)
  • Posterior:
    • Superior ulnar collateral artery (from the brachial artery)
    • Posterior ulnar recurrent artery (from the ulnar artery)
• Lateral Anastomosis:
  • Anterior:
    • Radial collateral artery (from the profunda brachii artery)
    • Radial recurrent artery (from the radial artery)
  • Posterior:
    • Middle collateral artery (from the profunda brachii artery)
    • Interosseous recurrent artery (from the posterior interosseous artery)
• Functional Importance:
  • Maintains normal circulation to forearm and hand during elbow flexion and temporary compression of the brachial artery.

This quiz explores the anatomy of the arm, focusing on its compartments and muscle innervations. It covers structures such as the ulnar and radial nerves, as well as the muscles located in the anterior compartment. Test your knowledge of the arm's anatomy and its key components.