Which is a hinge joint :
**Core Concept**
A hinge joint is a type of synovial joint that allows for movement in only one plane, resembling the opening and closing of a door. This type of joint is characterized by a pair of convex and concave articular surfaces that form an axis of rotation, enabling flexion and extension movements.
**Why the Correct Answer is Right**
A hinge joint functions by allowing the distal bone to move around a single axis, which is formed by the articulating surfaces of the bones. This type of joint is commonly found in the elbow, knee, and ankle. The movement in a hinge joint is restricted to flexion and extension, with minimal or no rotation, abduction, or adduction. The fibrous joint capsule and ligaments surrounding the joint provide stability and support.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because ball-and-socket joints allow for multi-directional movement, whereas hinge joints restrict movement to a single plane.
**Option B:** This option is incorrect because pivot joints allow for rotation around a single axis, but they do not have the same type of articulating surfaces as hinge joints.
**Option C:** This option is incorrect because saddle joints allow for movement in two planes, which is different from the restricted movement in hinge joints.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that hinge joints are commonly found in weight-bearing joints, such as the knee and ankle, where stability and support are crucial for movement and locomotion.
**Correct Answer: C. Elbow joint.**