Proximal Interphalangeal (PIP) Joints Definition

The proximal interphalangeal (PIP) joints are commonly known as the middle knuckles of the fingers. The thumb does not have a PIP joint.

In medical terminology, PIP joints are synovial joints located where two phalanges meet. Phalanges are the bones in the fingers, thumbs, and toes.

A PIP joint is a hinge joint, meaning that it bends and straightens along one plane with little to no side-to-side movement.

Arthritis in the PIP joints

Osteoarthritis or autoimmune arthritis, such as rheumatoid arthritis, can damage a PIP joint over time. A PIP joint can also degenerate due to post-traumatic arthritis caused by a past injury. Failure to promptly treat an injured PIP joint increases the likelihood of developing post-traumatic arthritis.

An arthritic PIP joint may:

  • Feel painful and/or stiff
  • Be tender
  • Look swollen
  • Have less range of motion

Arthritic damage to a PIP joint can be diagnosed by a physician. Diagnosis may be confirmed with medical imaging, such as an x-ray. Treatment recommendations will depend on the type of arthritis, and may include but not be limited to medications, occupational therapy, splinting, therapeutic injections, or—rarely—surgery.