Little Proximal Interphalangeal (PIP) Joint Anatomy

The Finger PIP Joint provides an articulation between:

• Proximal Phalanx: The bone of the index located between the metacarpophalangeal (MP) joint and the PIP joint.
• Middle Phalanx: The middle phalanx of the finger located between the metacarpophalangeal (PIP) joint and the DIP joint.
• At the PIP joint, the proximal phalanx has a convex shaped head, and the middle phalanx has a concave base.  The PIP joint has complex biomechanics in part because these bone surfaces are not perfectly congruent.

Ligaments

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

The flexor tendons crossing the Finger PIP joint are:

• FDP: This tendon flexes the MP, PIP, and DIP joints.
• FDS: This tendon flexes the MP and PIP joints.

The finger PIP joint type:

• The finger interphalangeal (PIP) joint is a uniaxial hinge (ginglymoid) joint. This joint allows the phalanges to have primarily 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 covered with articular cartilage
  • Structural components contain:
    • Articular cartilage - enables low friction movement
    • Ligaments – stabilize a functional range of motion
    • 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