Lecture Notes: Forum and Forearm Movement

Introduction

• Forum Function: Fine-tunes hand position for object manipulation in various activities
• Degree of Freedom: 1 (Pronation-Supination)
• Joints Involved: Proximal and Distal Radioulnar Joints (seen as one joint for pronation-supination)

Proximal Radioulnar Joint

• Radial Head Movement: Moves around the radial notch
• Anular Ligament: Secures radial head allowing it to spin without moving

Interosseous Membrane

• Broad flat membrane between radius and ulna
• Holds bones together and provides a surface for forearm function

Distal Radioulnar Joint

• Articulation: Ulna head articulates with ulnar notch of the radius
• Stability: Multiple stabilizing ligaments, including the Triangular Fibrocartilage Complex (TFCC)
• TFCC: Revisits in detail when discussing the wrist complex

Forearm Movement

• Pronation-Supination Axis: Virtual line from radial head to ulnar head
• Radial and Ulnar Movement: Radius moves over ulna predominantly; ulna moves very slightly (~3°)
• Normal Range of Motion: 0° to 80° (neutral to pronation/supination)
• Functional Range: 0° to 50° (for daily activities)
• Bone Injury: Radial bone fractures may reduce range of motion but often don’t severely affect function

Prime Movers for Forearm Movement

• Pronation:
  • Pronator Quadratus (distal forearm; large, square-shaped)
  • Pronator Teres (smaller, round muscle; efficient in fast/resisted pronation)
• Supination:
  • Biceps Brachii (most efficient at 90° elbow flexion)
  • Supinator (best function when elbow extended)

Associated Muscles

• Elbow Flexion: Biceps Brachii, Brachialis, Brachioradialis
• Elbow Extension: Triceps Brachii, Anconeus
• Forearm Pronation: Pronator Quadratus, Pronator Teres
• Forearm Supination: Biceps Brachii, Supinator

Common Elbow and Forearm Pathologies

• Epicondylitis:
  • Lateral Epicondylitis (Tennis Elbow): Overuse of wrist and hand extensors
  • Medial Epicondylitis (Golfer’s Elbow): Overuse of wrist and finger flexors
• Pulled Elbow (Nursemaid’s Elbow): Seen in young children; caused by a sudden pull on an extended arm (trauma to anular ligament)
• Dislocation: Less common, typically due to accidents or sports injuries
• Cubital Tunnel Syndrome: Ulnar nerve compression at the elbow; second most common nerve compression syndrome (after carpal tunnel at the wrist)