Hinge Joint between Humerus and Radioulna

A hinge joint is a type of synovial joint that allows movement in only one plane, similar to the hinge on a door. This type of joint is found in the elbow joint between the humerus (upper arm bone) and the radioulna (forearm bones - radius and ulna).

The Humerus:
The humerus is the bone of the upper arm and is the longest and largest bone in this region. It extends from the shoulder joint to the elbow joint. The distal end of the humerus forms two prominences called condyles. These are the medial condyle and the lateral condyle.

The Radioulna:
The radioulna consists of two bones - the radius and the ulna. The radius is located on the thumb side of the forearm, while the ulna is located on the little finger side. These bones run parallel to each other and are connected by a syndesmosis joint.

The Hinge Joint:
A hinge joint is a synovial joint that allows movement in only one plane, resembling the motion of a hinge. It enables flexion and extension movements, similar to opening and closing a door. The hinge joint between the humerus and the radioulna allows for the bending and straightening of the elbow.

Key Features of a Hinge Joint:
- Uniaxial joint: A hinge joint allows movement in only one plane, around a single axis.
- Articular surfaces: The articular surfaces of the bones involved in a hinge joint are shaped to fit together like a hinge, with one convex and one concave surface.
- Ligaments: Ligaments surround and support the hinge joint, providing stability and preventing excessive movement.

Function:
The hinge joint between the humerus and the radioulna allows for flexion and extension movements of the forearm at the elbow. When the arm is flexed, the forearm moves towards the upper arm, and when the arm is extended, the forearm straightens away from the upper arm.

Overall, the hinge joint between the humerus and the radioulna provides stability and enables the bending and straightening of the elbow joint, allowing for various activities involving the movement of the forearm.