The term “knuckle” is not a formal medical term but a common name for the rounded joints of the fingers. This non-specific term refers to several distinct joints within the hand, each serving a unique mechanical purpose. Locating these joints requires understanding their anatomical position relative to the bones of the palm and fingers.
Defining the Major Knuckles
The most prominent knuckles are those visible when clenching a fist. These joints are located where the fingers meet the palm, at the base of each digit. Anatomically, they are known as the Metacarpophalangeal (MCP) joints.
The MCP joints connect the heads of the long bones of the palm, called the metacarpals, to the top bones of the fingers. These joints allow for movement in two planes, which is crucial for gripping and manipulating objects.
The Smaller Knuckles
The fingers contain additional joints also referred to as knuckles, facilitating the curling motions necessary for grasping. These smaller joints are found along the length of the fingers. The four fingers each contain two of these smaller knuckles, while the thumb only has one.
Proximal Interphalangeal (PIP) Joint
The joint closest to the palm is the Proximal Interphalangeal (PIP) joint. This joint is found between the first and second bone of the finger and is responsible for a significant arc of flexion, essential for the hand’s powerful grip.
Distal Interphalangeal (DIP) Joint
The joint nearest the fingertip is the Distal Interphalangeal (DIP) joint. The DIP joint is the smallest of the knuckles and allows for the final, fine-tuning movements of the finger’s tip.
Skeletal Structure: The Bones That Form Knuckles
The knuckles are formed by the articulation of two main groups of bones. The bones of the palm are the five metacarpals, which extend toward the fingers. The bones within the fingers are called phalanges; each finger has three (proximal, middle, and distal), except for the thumb, which has two.
The MCP joint, or major knuckle, is formed by the rounded head of a metacarpal bone meeting the base of the proximal phalanx. The PIP joint is where the head of the proximal phalanx connects with the base of the middle phalanx. The DIP joint is created by the head of the middle phalanx meeting the base of the distal phalanx.