Thumb IP Joint Anatomy

The Thumb IP joint provides an articulation between:

• Proximal Phalanx: The bone of the thumb located between the metacarpophalangeal (MCP) joint and the IP joint.
• Distal Phalanx: The terminal bone of the thumb.

Ligaments

• Collateral Ligaments: The proper and accessory collateral ligaments are located on the ulnar and radial sides of the IP joint and stabilize the joint from side-to-side movements (lateral stress).
• Volar Plate: Located on the palmar side of the IP joint.  It prevents hyperextension and provides joint stability.

Tendons crossing the Thumb IP Joint:

• FPL: This tendon flexes the IP joint.
• EPL: This tendon extends the IP joint.

Thumb IP joint type:

• The thumb interphalangeal (IP) joint is a uniaxial hinge (ginglymoid) joint. This joint allows the phalanges to have a flexion/extension arc of motion.
• Synovial joint
  • Synovial joints are specialized structures that allow movement at bony articulations. 
  • Composed of a joint cavity lined by synovium containing bones lined with articular cartilage.
  • Structural components contain:
    • Articular cartilage - enables low friction movement
    • Ligaments
    • Joint capsule - fibrous tissue surrounding joint cavity
    • Synovium - tissue lining non-cartilaginous portions of joint cavity and is composed of two layers, the intimal lining and the connective tissue sublining
    • Synovial fluid - joint lubricant produced and regulated by the synovium