Elbow and Forearm Anatomy

• The elbow and forearm's anatomical structure consists of three bones: the lower end of the humerus, the radius, and the ulna.

Humerus (Lower End)

• Medial epicondyle serves as the attachment site for flexor muscles.
• Lateral epicondyle serves as the attachment site for extensor muscles.
• Trochlea is a pulley shape that attaches to the head of the radius, forming the ulnohumeral joint.
• Capitulum is a round shape that attaches to the head of the radius, forming the radiohumeral joint.
• Radial fossa, located above the capitulum, accommodates the head of the radius during elbow flexion.
• Coronoid fossa receives the olecranon process of the ulna when the elbow is extended.

Radius

• Lateral bone of the forearm
• It articulates superiorly with the humerus, forming the radiohumeral joint.
• It articulates medially with the ulna, forming the proximal radioulnar joint.
• It articulates distally with the scaphoid and lunate, forming the wrist joint.
• Radial head connects with the capitulum of the humerus superiorly and the radial notch of the ulna medially.
• Neck connects the head to the radial shaft.
• The shaft is wider below than above.
• Bicipital tuberosity is the insertion point for the biceps brachii muscle.
• Interosseous border serves as the attachment for the interosseous membrane.
• Pronator tubercle, located on the lateral side, is the insertion point for the pronator teres muscle.
• Radial styloid process is at the distal end.
• Ulnar notch attaches to the head of the ulna inferiorly, forming the distal radioulnar joint.
• Dorsal tubercle (Lister’s tubercle) is present on the dorsal side.

Ulna

• Medial bone of the forearm
• It articulates superiorly with the humerus to form the ulnohumeral joint.
• It articulates laterally with the radius to form the radioulnar joint.
• Olecranon process is the prominence of the elbow.
• Trochlear notch is anterior to the olecranon process and articulates with the trochlea of the humerus.
• Coronoid process is below the trochlear notch and articulates with the coronoid fossa of the humerus during elbow flexion.
• The shaft is wider above than below.
• Lateral/Interosseous border is present.
• Supinator crest serves as the attachment for the supinator muscle.
• Ulnar styloid process is present.
• Radial notch is on the lateral side of the coronoid process and attaches to the head of the radius.
• Ulnar head projects lateral to the ulnar styloid process.

Joints of the Forearm

• Superior (Proximal) Radioulnar joint
• Middle Radioulnar joint
• Distal (Inferior) Radioulnar joint

Cubital Articulations

• Radiohumeral joint
• Ulnohumeral joint
• Superior (Proximal) Radioulnar joint

Elbow Joints

• The elbow joint is a synovial hinge joint formed by two joints: the ulnohumeral and radiohumeral joints.
• Ulnohumeral joint (Humeroulnar joint): Articulation between the trochlea of the humerus and the trochlear notch of the ulna.
• Radiohumeral joint (Humeroradial joint): Articulation between the capitulum of the humerus and the head of the radius.

Ligaments of the Elbow

• Radial/Lateral Collateral Ligament
  • Cord-like structure attaching at the lateral epicondyle and the base of the annular ligament.
  • Primary restraint to posterolateral instability, resisting varus force.
• Ulnar/Medial Collateral Ligament
  • Fan-shaped ligament resisting valgus force, with three bands:
    • Anterior Band: Attaches at the medial epicondyle to the medial margin of the coronoid process.
    • Posterior Band: Attaches at the medial epicondyle to the medial side of the olecranon.
    • Transverse/Oblique Band: Located between the attachments of the anterior and posterior bands.
  • Nerve supply: Musculocutaneous, Median, Ulnar, and Radial nerve.
• Movements include:
  • Flexion: Biceps brachii, Brachioradialis, Brachialis, Pronator Teres.
  • Extension: Triceps brachii and Anconeus.
• Normal functional position of the elbow is 90° of elbow flexion with the forearm midway between supination and pronation.
• Forearm functional position: forearm slightly pronated
• Triangle Sign:At 90° of elbow flexion, the olecranon process, medial and lateral epicondyle forms an isosceles triangle, but when the elbow is fully extended, the three points normally form a straight line
• Carrying Angle:
  • Formed by the longitudinal axis of the arm and forearm.
  • The ulnohumeral joint determines the carrying angle.
    • Normal Value: Male: 5-10 degrees; Female: 10-15 degrees
  • Increased angle: Cubitus Valgus is present which may be caused by a lateral supracondylar fracture.
  • Decreased angle: Cubitus Varus is present which may be caused by a Gunstock deformity.
• Cubital (Ulnar) Tunnel
  • A fibro-osseous space on the posteromedial aspect of the elbow, formed between the medial epicondyle and the olecranon process.
  • The ulnar nerve runs through it and can be compressed, known as the "Funny bone".
  • Compression of the ulnar nerve at the ulnar groove Leads to cubital tunnel syndrome

Mechanism of Injury

• Injury may lead to:
  • Stretching of the medial collateral ligament
  • Stress on the epicondylar growth plate (Pitcher’s or Little Leaguer’s Elbow)
  • Compression at the radiohumeral joint
  • Compression of the olecranon fossa, which may lead to osteophyte and loose formation