The human hand is a marvel of biological engineering, capable of both powerful grips and delicate, precise movements. Knuckles are prominent features that facilitate the hand’s wide range of motion, enabling daily activities from writing to lifting. Understanding what constitutes a knuckle and how many we possess offers insight into the intricate design of our hands.
What is a Knuckle?
In everyday conversation, a “knuckle” typically refers to the rounded, visible joints of the fingers, especially those at the base of the fingers when a fist is made. Anatomically, however, the term encompasses the various joints found within the fingers and thumb. These joints are points where two or more bones meet, allowing for movement.
The joints commonly identified as knuckles include the metacarpophalangeal (MCP) joints and the interphalangeal (IP) joints. MCP joints are located at the base of the fingers, connecting the long bones of the hand (metacarpals) to the first set of finger bones (proximal phalanges). These joints enable the fingers to bend, straighten, spread apart, and come together.
Further along each finger are the interphalangeal joints. There are two types: the proximal interphalangeal (PIP) joints and the distal interphalangeal (DIP) joints. PIP joints are situated in the middle of each finger, while DIP joints are found closer to the fingertip. These joints act like hinges, primarily allowing the fingers to bend and extend.
Counting Your Knuckles
To count the knuckles, or joints, of the hand, examine each digit individually. The four fingers—index, middle, ring, and pinky—share a similar structure. Each contains three distinct joints, including one metacarpophalangeal (MCP) joint at its base, which connects to the hand.
Moving distally along each finger, there is also one proximal interphalangeal (PIP) joint in the middle segment and one distal interphalangeal (DIP) joint closest to the fingertip. Therefore, each of these four fingers contributes three joints. With four fingers, this totals 12 joints (3 joints/finger x 4 fingers).
The thumb, however, has a unique configuration compared to the other fingers. It is composed of only two bones, or phalanges, meaning it has two joints. These include one metacarpophalangeal (MCP) joint at its base, connecting it to the hand, and a single interphalangeal (IP) joint.
Combining the count for all digits on one hand reveals the total number of knuckles. The 12 joints from the four fingers, plus the 2 joints from the thumb, result in a total of 14 joints on a single hand. Extending this count to both hands, a person typically has 28 knuckles in total (14 joints/hand x 2 hands).