What is a bursae?

A bursae is indeed best described as a fluid-filled closed sac. Bursae are small, synovial fluid-filled sacs located throughout the body, often found in areas where friction might occur, such as between bones and tendons or muscles. Their primary function is to cushion and reduce friction between these structures during movement, helping to facilitate smooth motions in joints.

Understanding this definition is key in the context of joint biomechanics and injury prevention, as bursae play a crucial role in reducing wear and tear on tissues. For instance, when inflammation occurs in a bursae, it can lead to bursitis, a painful condition that impacts joint mobility.

The other choices do not accurately reflect the anatomical structure or function of bursae. A type of joint refers to the connections between bones rather than a fluid-filled structure, while a ligament is a connective tissue that connects bones to other bones, and cartilage provides cushioning between bones at a joint but does not have the characteristics of a bursae.