Which of the following is an example of a synovial (diarthrosis) joint?

• A. Knee joint
• B. Sutures of the skull
• C. Intervertebral discs
• D. Gomphosis of teeth

Answer: (A)

Synovial joints have a joint cavity enclosed by a capsule, with articular cartilage on the joint surfaces and synovial fluid inside, allowing free, multiple-direction movement (diarthrosis). The knee fits this model, featuring a synovial cavity, a fibrous capsule reinforced by ligaments, menisci, and articular cartilage on the femur, tibia, and patella, all enabling wide flexion, extension, and some rotation.

In contrast, sutures of the skull are fibrous joints with dense connective tissue and no joint cavity, providing stability but little to no movement. Intervertebral discs form a cartilaginous joint (a symphysis) where a fibrocartilaginous disc cushions between vertebrae, limiting movement. Gomphosis of teeth is also a fibrous joint, with teeth anchored by the periodontal ligament and no joint cavity. Thus, the knee is the example of a synovial (diarthrosis) joint.