Which digit has only one interphalangeal joint?

The hallux, or big toe, is unique among the digits in that it has only one interphalangeal joint. This joint is located between the proximal phalanx and the distal phalanx of the hallux, allowing for a limited range of motion primarily focused on flexion and extension.

In contrast, the other digits—index, middle, and pinky—each have two interphalangeal joints: a proximal interphalangeal joint and a distal interphalangeal joint. These additional joints enhance the dexterity and functionality of the fingers, allowing for more intricate movements and grip capabilities. The distinction of the hallux having a single interphalangeal joint is significant in understanding foot mechanics and the role of toes in balance and gait.