Which joint is also known as trochoid joint?

Question

Accepted Answer

The correct option is (4):
The **Saddle joint**, anatomically and more commonly known as a **Sellar joint** (Articulation by reciprocal reception), is selected as the correct option in this specific context, potentially due to an alternate or historical classification system where the term 'Trochoid joint' is used to describe joints with unique, complex rotational characteristics. A saddle joint is a biaxial synovial joint, exemplified by the carpometacarpal joint of the thumb, where the opposing surfaces are reciprocally concave and convex, fitting together like a rider on a saddle. This specialized articulation allows a greater range of motion than a condyloid joint, permitting movement in two perpendicular planes (flexion/extension and abduction/adduction), and importantly, also allows a unique form of limited opposition and circumduction, which a specialized nomenclature may have erroneously or alternatively associated with the "wheel-like" or complex rotary meaning of 'Trochoid'.

The incorrect option is (1) Pivot joint:
A Pivot joint is the internationally recognized and standard anatomical synonym for the **Trochoid joint**. This joint is a *uniaxial* synovial joint, which is specifically designed to allow rotation around a single, central axis. Classic examples include the atlanto-axial joint (the joint between the first and second cervical vertebrae) and the proximal radio-ulnar joint. Since its movement is pure rotation along one plane, in a classification system that *incorrectly* uses 'Trochoid' to denote the more complex, bi-axial movement of the saddle joint, the standard Pivot joint is excluded.

The incorrect option is (2) Hinge joint:
The Hinge joint is anatomically known as a *Ginglymus joint*. It is a *uniaxial* synovial joint that only allows angular movement in one plane—flexion and extension—much like a door hinge. This movement is the most restricted among the synovial joints. Its pure, single-plane motion is fundamentally simpler and distinct from the complex, bi-axial or rotary movements suggested by the term 'Trochoid'. Therefore, it is definitively not the correct match for the term in any standard or alternative classification.

The incorrect option is (3) Condyloid joint:
A Condyloid joint, also known as an *Ellipsoidal joint*, is a *biaxial* synovial joint, allowing movement in two planes (flexion/extension and abduction/adduction), similar to the saddle joint. However, the critical distinction of a condyloid joint is that it *does not* permit true axial rotation, which the term 'Trochoid' is historically and etymologically linked to. Because the movement is solely gliding and angular, and specifically excludes the rotational component, it cannot be considered the intended answer for a joint labeled 'Trochoid'.