**Core Concept**
The 1st carpometacarpal joint is a unique joint in the human body, characterized by a saddle-shaped joint that allows for a wide range of motion. This joint is formed between the trapezium bone of the wrist and the 1st metacarpal bone of the thumb.

**Why the Correct Answer is Right**
The 1st carpometacarpal joint is a type of condyloid joint, which is a joint that allows for movement in two planes. The saddle-shaped joint is made possible by the unique shape of the trapezium bone, which has a concave surface that articulates with the convex surface of the 1st metacarpal bone. This joint is essential for thumb movement, allowing for opposition, flexion, extension, abduction, and adduction. The ligaments and muscles surrounding this joint provide stability and support for its unique range of motion.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the 1st carpometacarpal joint is not a ball-and-socket joint, which is a different type of joint that allows for three-dimensional movement.
* **Option B:** This option is incorrect because the 2nd carpometacarpal joint is actually a type of arthrodesis, which is a joint that has been fused together, and does not allow for movement.
* **Option C:** This option is incorrect because the 3rd carpometacarpal joint is actually a type of saddle joint, but it is not the 1st carpometacarpal joint.

**Clinical Pearl / High-Yield Fact**
The 1st carpometacarpal joint is prone to osteoarthritis, particularly in women, due to the increased stress and wear and tear on the joint. This can lead to pain and stiffness in the thumb, and may require surgical intervention in severe cases.

**Correct Answer: C. Saddle joint.**