Carpometacarpal joint is an example of which of the following types of joints?

AIIMS Patna NO - 2020

Applied Physiology

Easy

Appeared in: AIIMS Patna NO - 2020

Explanation

The carpometacarpal joint of the thumb is classified as a saddle (sellar) joint.
Its articular surfaces are reciprocally concavo-convex, meaning each surface has both a concave and a convex area, fitting together like a rider on a saddle.
This biaxial joint structure allows for flexion, extension, abduction, adduction, and circumduction.
Crucially, the saddle shape facilitates opposition, the movement that allows the thumb to touch the other fingertips, which is fundamental to human dexterity.

Option A: A hinge joint (ginglymus) is uniaxial and only permits movement in one plane (flexion and extension), like the opening and closing of a door. The thumb's CMC joint has a much wider range of motion.
Option B: A ball and socket joint is multiaxial, allowing movement in all planes, including rotation. While the thumb has great mobility, its CMC joint is biaxial and does not have the same extensive rotation as a true ball and socket joint.
Option C: A pivot (trochoid) joint is uniaxial and only allows for rotation around a single longitudinal axis. The thumb's CMC joint performs flexion/extension and abduction/adduction, not just rotation.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of synovial joints as background academic context rather than a clinical decision trigger.
Nurses frequently assess hand function. Understanding that the thumb's CMC joint is a saddle joint explains why it is so mobile but also susceptible to degenerative conditions like osteoarthritis.
Pain and instability at the thumb CMC joint can severely limit a patient's ability to perform activities of daily living (ADLs) such as writing, opening jars, or buttoning a shirt.
What if? If the thumb's carpometacarpal joint were a hinge joint instead of a saddle joint, the thumb would only be able to flex and extend. The ability to oppose the thumb to the fingers would be lost, and the human hand would lose its unique ability to grasp and manipulate objects with precision.

How to Approach the Question

First, identify the key term in the question: 'Carpometacarpal joint'.
Recall the different classifications of synovial joints (plane, hinge, pivot, condyloid, saddle, ball and socket).
Associate the carpometacarpal joint of the thumb with its specific classification. It is a classic textbook example.
Consider the type of movement the thumb can make at its base: it moves forward/backward, side-to-side, and can touch the other fingers (opposition). This multi-planar movement rules out uniaxial joints like hinge and pivot.
Differentiate between saddle and ball-and-socket. The thumb's movement is primarily biaxial with some rotation (opposition), which perfectly matches the description of a saddle joint. A ball-and-socket joint allows for more extensive rotation.
Select the option that correctly classifies the joint based on its structure and function.

Concept Tested & Keywords

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E6 Anatomy Applied Ashalatha 4e p. 297-299

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