What type of joint contains a cavity filled with synovial fluid and is freely movable?

• A. Synovial joint
• B. Fibrous joint
• C. Cartilaginous joint
• D. Amphiarthrosis

Answer: (A)

Synovial joints are the ones that have a joint cavity filled with synovial fluid, and this arrangement makes the joint freely movable. The cavity sits inside the joint capsule and is lubricated by the synovial fluid, which reduces friction and nourishes the articular cartilage on the ends of the bones. This combination—a fluid-filled cavity plus a robust capsule and ligaments—defines a diarthrosis, or freely movable joint. In contrast, fibrous joints lack a joint cavity and are typically rigid or only slightly movable, while cartilaginous joints use cartilage to connect bones and are usually immovable or only somewhat movable and do not contain a synovial cavity. The term amphiarthrosis describes joints that are only slightly movable, often associated with cartilaginous connections, and does not describe a cavity-filled, highly movable joint.