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How do knuckle-walking and digitigrade quadrupedalism differ?

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Illustration comparing the body plans of representative anthropoids, showing a male western lowland gorilla, a male human, a male bonobo, a female Bornean orangutan, and male and female northern white-cheeked gibbons, all labeled and depicted to scale. — primate Representative apes (superfamily Hominoidea).

Knuckle-walking and digitigrade quadrupedalism are distinct modes of terrestrial locomotion characterized by different contact points between the limbs and the ground.

Knuckle-walking: This is a form of quadrupedalism observed in great apes, such as chimpanzees and gorillas. When these animals move on the ground, they support their trunks by placing the knuckles of their outstretched forelimbs on the ground. This adaptation is associated with their elongated forelimbs.1
Digitigrade Quadrupedalism: In this posture, an animal walks on its toes, with the phalanges (fingers and toes) touching the ground while the ankle and wrist remain elevated. Examples of mammals that utilize this gait include dogs and cats.2

While both involve four-legged movement, they differ fundamentally in the anatomy of the contact surface: knuckle-walking utilizes the dorsal surface of the finger joints, whereas digitigrade locomotion relies on the tips of the digits. It is important to note that these categories are behavioral and anatomical classifications used to describe how different species interact with their environment during movement.123