Saddle joint

Recommended video: Types of synovial joints [18:19]

Synovial joints are the main type of joints found in the body.

Saddle joints, sometimes called sellar joints, are a type of synovial joint formed between convex and concave articulating surfaces, interlocking like two saddles opposed to one another.

Similar to condyloid joints, saddle joints usually allow movement with two degrees of freedom. Specifically, they allow flexion and extension, abduction and adduction as well as circumduction.

The first carpometacarpal joint or trapeziometacarpal joint is a synovial saddle joint. It is a multiaxial joint, allowing the movements in three degrees of freedom: flexion and extension, abduction and adduction and some axial rotation. It is the combination of this joint and our elongated thumbs that allow us to oppose the thumb and therefore perform complex tasks with our hands.

Two other examples of synovial saddle joints are the sternoclavicular joint and the incudomalleolar joint. The former is a joint connecting the sternum with the clavicles. It is the only direct connection between the appendicular skeleton of the upper limb and the axial skeleton of the trunk. The latter is also known as the incudomallear joint and comprises the articulation between the incus and the malleus. The joint is part of the chain of ossicles sending vibrations from the tympanic membrane to the vestibular window.