Anatomy of Forearm and Hand Structures

Joint Classifications

Understanding how these bones move is essential for clinical reasoning:

• Radiocarpal joint: An ellipsoid joint where the scaphoid, lunate, and triquetrum articulate with the distal radius and articular disc.
• Intercarpal joints: Gliding synovial joints between adjacent carpal bones.
• Midcarpal joint: The articulation between the proximal and distal rows.
• Thumb CMC joint: A saddle joint (trapezium + 1st metacarpal) that allows for opposition.
• MCP joints (digits 2-5): Condyloid joints.
• Interphalangeal joints: Hinge joints.

Forearm and Elbow Soft Tissues

The stability of the elbow and the movement of the forearm depend on specific ligaments and muscle groups.

Elbow Ligaments and Nerves

The elbow is stabilized by the ulnar collateral ligament on the medial side (which resists valgus stress) and the radial collateral ligament on the lateral side. The annular ligament is a ring-like structure that secures the head of the radius against the ulna.

When palpating the medial elbow, be mindful of the ulnar nerve, which runs behind the medial epicondyle (often referred to as the "funny bone"). Additionally, the olecranon bursa is a fluid-filled sac located directly over the olecranon process at the back of the elbow.

The "Wad of Three"

On the lateral aspect of the forearm, there is a specific group of muscles often referred to as the "Wad of Three". These include:

1. Brachioradialis
2. Extensor Carpi Radialis Longus
3. Extensor Carpi Radialis Brevis

Hand Eminences and the Palmar Surface

The fleshy parts of the hand provide essential landmarks for palpation.

• Thenar eminence: The large muscle mound at the base of the thumb.
• Hypothenar eminence: The smaller muscle mound at the base of the little finger.
• Palmar aponeurosis: A thick, fan-shaped layer of connective tissue located in the center of the palm.

Specialized Regions: Carpal Tunnel and Snuffbox

Two of the most high-yield areas for anatomy exams are the carpal tunnel and the anatomical snuffbox.

The Carpal Tunnel

The carpal tunnel is a passageway at the palmar wrist.

• Roof: Formed by the flexor retinaculum.
• Floor/Walls: Formed by the carpal bones.
• Contents: The median nerve and nine flexor tendons.
  • The nine tendons consist of: 4 Flexor Digitorum Superficialis, 4 Flexor Digitorum Profundus, and 1 Flexor Pollicis Longus.

Note that the extensor retinaculum serves a different purpose, acting as a band across the back (dorsal) of the wrist to hold the extensor tendons in place.

The Anatomical Snuffbox

This is a visible depression on the thumb side of the wrist, seen clearly when the thumb is extended.

• Radial Border: Formed by the Abductor Pollicis Longus and Extensor Pollicis Brevis.
• Ulnar Border: Formed by the Extensor Pollicis Longus.
• Floor: Primarily the scaphoid bone.
• Vessel: The radial artery passes through this space.

Summary Table for Quick Review

Practical Exam Strategy When performing palpation, always orient yourself first. Identify the side (right/left) and the plane (anterior/posterior, medial/lateral) before touching the landmark. Build a "route" in your mind: start with a bone, move to a landmark, and then identify the muscle or nerve.