Which structure is commonly associated with the protection of the bone ends?

Articular cartilage is indeed the correct answer as it plays a crucial role in protecting the ends of bones at synovial joints. This smooth, white tissue covers the surfaces of bones where they come together to form joints, providing a cushioning layer that reduces friction during movement. By allowing bones to glide over one another smoothly, articular cartilage helps prevent wear and tear on the underlying bone tissue.

In addition to its protective role, articular cartilage also assists with shock absorption, which is vital for maintaining joint health and function. As joints experience different loads and movements, the presence of articular cartilage helps to evenly distribute these forces across the joint surface.

The medullary cavity, periosteum, and endosteum all serve distinct functions related to bone structure and health, but they are not primarily involved in the protection of bone ends at joints. For instance, the medullary cavity contains bone marrow and is primarily associated with blood cell production; the periosteum is a dense layer of vascular connective tissue that envelops the bones except at surfaces of joints, providing a site for muscle attachment; and the endosteum lines the medullary cavity and is involved in bone growth, repair, and remodeling. Each of these elements contributes to the