What type of synovial joint is primarily responsible for flexion and extension?

• A. Pseudarthrotic
• B. Hinge
• C. Ball and socket
• D. Diarthrotic

Answer: (B)

The hinge joint is specifically designed to allow movement primarily in one plane, which facilitates flexion and extension. This type of synovial joint resembles the mechanism of a door hinge, permitting movement that occurs around a single axis. An excellent example of a hinge joint is found in the elbow, where the forearm can flex towards the upper arm or extend away from it.

In contrast, a ball and socket joint allows for a greater range of motion, enabling movements in multiple planes, including rotation, which goes beyond just flexion and extension. Pseudarthrotic joints, typically non-functional due to incomplete union of bone, do not facilitate typical joint movement. Lastly, while diarthrotic joints encompass all synovial joints (including hinge and ball and socket), they do not specify the type of movement, making "hinge" the most accurate answer for the primary capability of flexion and extension.