What connective tissue structure surrounds a diarthrodial joint?

The connective tissue structure that surrounds a diarthrodial joint is a capsule. This structure is known as the articular capsule and serves a vital role in maintaining the integrity and function of the joint. It is composed of two layers: an outer fibrous layer that provides stability and protection, and an inner synovial membrane that produces synovial fluid. This fluid lubricates the joint, reduces friction, and nourishes the cartilage within the joint. The capsule also helps to restrict excessive movement, thereby contributing to joint stability and proper alignment during motion.

While tendons connect muscles to bones and help facilitate movement, and ligaments connect bones to other bones and provide support, these structures do not encompass the joint itself. Cartilage is found within the joint, providing cushioning and facilitating smooth movement, but it does not serve as an enclosing structure. Thus, the capsule is the correct choice as it encapsulates the joint, making it essential for a diarthrodial joint's functionality.