What is an immovable joint known as?

An immovable joint is referred to as a synarthrosis. This type of joint is characterized by the absence of movement between the connected bones. Synarthroses allow for stability and protect the underlying structures, making them crucial in areas where support and strength are needed, such as in the skull, where the bones are tightly fused together. This fusion forms sutures, which are a specific type of synarthrosis.

In contrast, amphiarthrosis describes joints that allow for limited movement, such as those found in the intervertebral discs of the spine. Diarthrosis refers to freely movable joints, like the knee and elbow, which enable a wide range of motion. A hinge joint, while a type of diarthrosis, specifically allows movement in one plane, much like how a door opens and closes. Therefore, synarthrosis stands out as the correct term for immovable joints.