The simple answer to the question of whether a dog has four knees is no. A dog, like a human, possesses two knees located on its two hind legs. The common confusion stems from the overall appearance of a dog’s limbs, where the structure and orientation of its joints differ significantly from human anatomy. This difference creates the illusion of multiple knee-like joints that appear to bend in unusual directions. Canine anatomy is adapted for efficient quadrupedal locomotion, which repositions the joints relative to the ground compared to a human’s upright posture.
Identifying the Canine Knee Joint
The true knee joint in a dog’s hind leg is called the stifle, which is directly analogous to the human knee. It connects the major bones of the upper and lower leg, formed by the articulation of the femur (thigh bone) and the tibia and fibula. The stifle is a complex joint that operates primarily as a hinge, allowing for the leg’s flexion and extension, which is essential for movement. Like the human knee, the stifle also contains a small, almond-shaped bone called the patella, or kneecap. The stifle is typically positioned higher on the dog’s body, often partially obscured by muscle and fur, contributing to its less obvious appearance.
The Joints of the Hind Leg
The second, lower joint in the dog’s hind leg is the primary source of the “four knees” misconception. This joint is not a second knee but is correctly identified as the hock, or the tarsus, which is the anatomical equivalent of the human ankle. The hock joint is made up of several small tarsal bones that connect the tibia and fibula to the metatarsal bones of the foot. The hock appears to bend backward like a reversed knee due to the dog’s digitigrade stance. Dogs walk on their toes with their heel and ankle elevated off the ground, unlike humans who have a plantigrade stance.
Why the Forelegs Look Like They Have Knees
The front legs also have two prominent joints that are often mistaken for knees, but they are actually the elbow and the carpus. The joint higher up on the foreleg is the elbow, which connects the humerus, the upper arm bone, to the radius and ulna of the forearm. The elbow acts as a hinge joint, allowing for the forward and backward swing of the front leg.
The Carpus (Wrist)
The joint lower down on the foreleg, which bends forward, is the carpus, which is the dog’s wrist. The carpus is comprised of seven short carpal bones arranged in two rows, providing stability and flexibility for weight bearing. Like the hock in the rear leg, the carpus is elevated because the dog stands on its digits. The resulting angles, combined with the digitigrade posture, visually confuse observers accustomed to the flatter, plantigrade arrangement of human limbs.