When convex surface fits into concave surface, this is called as

Appeared in: UPPSC 2017

Explanation

A hinge joint (or ginglymus) is structurally defined by a convex surface of one bone fitting into a corresponding concave surface of another bone.
This specific shape restricts movement to a single axis, much like a door hinge.
Consequently, hinge joints are uniaxial, allowing only for flexion and extension.
Classic examples in the human body include the elbow joint (humeroulnar articulation) and the interphalangeal joints of the fingers and toes.

Option A: A plane joint is incorrect because its articulating surfaces are flat or only slightly curved, not a distinct convex-concave pairing. This structure allows for gliding or sliding movements.
Option B: A saddle joint is incorrect because both of its articular surfaces are reciprocally concavo-convex (shaped like a rider in a saddle). This is a more complex arrangement than a simple convex-concave fit.
Option D: A ball and socket joint is incorrect because, while it does involve a convex 'ball' fitting into a concave 'socket', this specific terminology refers to a multiaxial joint that allows movement in all planes. The question describes the simpler, uniaxial hinge mechanism.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of synovial joints based on the shape of their articular surfaces as background academic context rather than a clinical decision trigger.
Understanding joint classification is crucial for a nurse when performing a musculoskeletal assessment, particularly for evaluating a patient's range of motion (ROM) and identifying the type of movement expected at each joint.
This knowledge helps in recognizing abnormal movements or limitations that may indicate injury, inflammation (like arthritis), or other pathologies.
What if? If a patient has rheumatoid arthritis affecting their finger joints (interphalangeal joints, which are hinge joints), the nurse would expect to find pain, swelling, and stiffness primarily during flexion and extension of the fingers, rather than side-to-side movements.

How to Approach the Question

First, identify the key descriptive terms in the question: 'convex surface' and 'concave surface'.
Next, recall the basic structural classifications of synovial joints.
Evaluate each option against the description provided in the stem.
A Plane joint has flat surfaces, which does not match.
A Saddle joint has reciprocally concavo-convex surfaces, which is more complex than the description.
A Hinge joint is defined by a convex surface fitting into a concave one, allowing uniaxial movement. This is a direct match.

Concept Tested & Keywords

Concept Tested: Classification of synovial joints based on the shape of their articular surfaces.
Stem keywords: convex surface, concave surface, joint
Lead-in keywords: is called as

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Practise the full UPPSC 2017

Attempt every question from this paper in a timed mock, then review the full solution for each one.