The stifle joint is the dog’s equivalent of the human knee — a hinge joint where the thigh bone (femur) meets the shin bone (tibia) and the kneecap (patella). Four key ligaments provide stability: the cranial cruciate, caudal cruciate, medial collateral, and lateral collateral. Two shock-absorbing pads of cartilage, the medial and lateral menisci, cushion the space between the femur and tibia. When osteoarthritis develops, joint cartilage gradually breaks down — leading to bone-on-bone friction, the formation of bone spurs, and chronic pain.