Carpometacarpal joint of thumb is
**Core Concept**
The carpometacarpal joint of the thumb is a specialized joint that allows for a wide range of motion, enabling the thumb to oppose the other fingers and participate in delicate manipulative tasks. This joint is a type of saddle joint, characterized by a unique bony morphology that enables its exceptional mobility. The carpometacarpal joint of the thumb is located at the base of the thumb, where the first metacarpal bone articulates with the trapezium bone in the wrist.
**Why the Correct Answer is Right**
The carpometacarpal joint of the thumb is a saddle joint due to the specific shape of the articulating bones. The trapezium bone has a saddle-shaped surface that matches the concave surface of the first metacarpal bone, allowing for a wide range of motion in multiple planes. This unique joint anatomy enables the thumb to move in a way that is not possible in other joints, making it essential for fine motor tasks such as grasping and manipulating objects.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the carpometacarpal joint of the thumb is not a ball-and-socket joint, which is characterized by a spherical head articulating with a cupped surface.
* **Option B:** This option is incorrect because the carpometacarpal joint of the thumb is not a hinge joint, which allows for movement in only one plane.
* **Option C:** This option is incorrect because the carpometacarpal joint of the thumb is not a condyloid joint, which allows for movement in two planes but does not have the specialized shape of the carpometacarpal joint.
**Clinical Pearl / High-Yield Fact**
A key aspect of the carpometacarpal joint of the thumb is its high mobility, which makes it susceptible to injuries such as thumb sprains and osteoarthritis. A common condition affecting this joint is osteoarthritis, which can lead to pain and stiffness in the thumb.
**Correct Answer: D. Saddle joint**