Anatomy and Movement of the Hand Joints

Key Bones and Joints

• Carpal Bones: Key bone is the capitate
• Metacarpal Bones: Form the CMC (Carpometacarpal) joint with the capitate
• Proximal Phalanges: Form the MCP (Metacarpophalangeal) joint with the metacarpal bones
• Joints: CMC, MCP, PIP (Proximal Interphalangeal), and DIP (Distal Interphalangeal) joints

CMC Joint (Carpometacarpal Joint)

• 2nd and 3rd CMC: Almost immobile
• Thumb CMC and 4th & 5th CMC: More mobile
• Movements: Involved in making a power grip and thumb opposition

Thumb CMC Motion

• Type of Joint: Saddle joint
• Movements:
  • Palmar Abduction: Moving thumb up towards the ceiling (may also be called simply abduction)
  • Radial Abduction: Moving thumb outward or away (also called extension in some texts)
  • Adduction: Moving thumb back from radial abduction
  • CMC Flexion: Bending the thumb to touch the palm
  • Opposition: Using the thumb pad to touch the other fingers

Confusing Terminology

• Palmar Abduction vs Abduction: Same movement but named differently in textbooks
• Radial Abduction vs Extension: Same movement but named differently in textbooks
• Adduction: Moving back from radial abduction
• Importance: Understanding these terminologies is crucial for clarity

MCP Joint (Metacarpophalangeal Joint)

• Structure: Convex with concave joint surface
• Stability: Relies on collateral ligaments (Radial Collateral Ligament and Ulnar Collateral Ligament)
  • Tightness: Collateral ligaments are tight when MCP is flexed at 90°
  • Post-Injury: MCP should be positioned in flexion to ensure ligaments remain tight and prevent shortening
• Movements: Flexion, extension, abduction, adduction, and some individuals may exhibit hyperextension

IP Joint (Interphalangeal Joint)

• Types: PIP (Proximal Interphalangeal) and DIP (Distal Interphalangeal) joints in fingers, and one IP joint in the thumb
• Movements: Flexion and extension
• Stability: Relies on collateral ligaments

Important Points

• Post-Injury Positioning: Hands should be positioned with MCP in 90° flexion to maintain ligament tightness and joint stability.
• Functionality: Proper functioning of these joints is essential for fine motor skills and object manipulation.