Medical Terminology for the Knuckle
The knuckle is medically termed the metacarpophalangeal (MCP) joint when referring to the junction between the metacarpal bones and the proximal phalanges (the prominent knuckles visible when making a fist), or the interphalangeal (IP) joints when referring to the joints between finger bones.
Anatomical Nomenclature
The term "knuckle" encompasses several distinct joint types depending on location:
Metacarpophalangeal (MCP) joints: The primary knuckles at the base of each finger where the metacarpal bones of the hand meet the proximal phalanges of the fingers 1
Proximal interphalangeal (PIP) joints: The middle knuckles of the fingers, located between the proximal and middle phalanges 1
Distal interphalangeal (DIP) joints: The knuckles closest to the fingertips, between the middle and distal phalanges 1
Clinical Context
In medical documentation and imaging, these joints are specifically identified by their anatomical names rather than the colloquial term "knuckle":
Ultrasound and radiographic imaging protocols reference these joints by their precise anatomical terminology (MCP, PIP, DIP) for accurate localization of pathology 1
The MCP joints are most commonly affected in conditions like rheumatoid arthritis, while DIP and PIP joints are characteristic targets in hand osteoarthritis 1
When examining hand pathology, the distribution pattern across these specific joint types provides diagnostic information—for example, DIP joint involvement is typical of osteoarthritis, whereas MCP joint involvement suggests inflammatory arthropathy 1
Common Pitfalls
The term "knuckle pads" refers to a distinct entity—benign thickening of skin overlying the PIP joints (not the joints themselves)—and should not be confused with the joints proper 2, 3, 4