The type of joint (pivot) between Atlas and Axis is known as

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Correct — D, Synovial joint. The Atlas (C1) and Axis (C2) vertebrae articulate at the atlanto-axial joint, a pivot joint — and pivot joints are one of the freely-movable synovial joint types (fluid-filled joint cavity, articular cartilage, enclosing capsule). The odontoid process (dens) of the Axis rotates within a ring formed by the Atlas, letting the head turn side to side.

Why the other options are wrong — (a) A saddle joint is a different synovial sub-type (e.g. the thumb's carpometacarpal joint) that allows back-and-forth and side-to-side movement, not rotation — it is not the Atlas-Axis joint.  (b) Fibrous joints (e.g. skull sutures) are fixed/immovable, connected by dense connective tissue with no joint cavity — the opposite of the freely-rotating Atlas-Axis joint.  (c) Cartilaginous joints (e.g. between vertebral bodies via intervertebral discs, or the pubic symphysis) allow only slight movement and lack a synovial cavity — they are not pivot joints.

Concept: Joints are classified by structure into fibrous (immovable), cartilaginous (slightly movable) and synovial (freely movable). Synovial joints are further divided by shape into hinge, pivot, ball-and-socket, saddle, gliding and condyloid types. A pivot joint lets one bone rotate around another — the clearest example is the atlanto-axial joint, which lets the head rotate.

State PCS 2022 Q1 — Science & Technology PYQ with Answer

State PCS 2022 Q1 — Science & Technology PYQ with Answer