Which of the following is an inflammation of the protective membranes surrounding a joint?

The correct answer is synovitis, which refers specifically to the inflammation of the synovial membrane, the protective lining that surrounds a joint. This condition can result in pain, swelling, and stiffness in the affected joint, as the synovial membrane plays a crucial role in producing synovial fluid, which lubricates and nourishes the cartilage and other tissues within the joint.

Understanding the context of the other terms clarifies why synovitis is the appropriate answer. Arthritis describes a broader category of conditions that involve inflammation of one or more joints, which may include synovitis as part of its presentation but is not limited to just that membrane. Tendinitis refers to the inflammation of the tendons, which are the tissues connecting muscles to bones and are not related to the joint membranes. Osteitis involves inflammation of the bone, which is again a different structure from the joint's protective membranes. By focusing on the specific role and definition of synovitis, it is clear why this is the correct term for inflammation of the protective membranes surrounding a joint.