**Core Concept**
A fracture of necessity refers to a fracture that requires an associated injury to another bone or structure for its stability, as the fracture itself is insufficient to maintain the integrity of the surrounding anatomy.

**Why the Correct Answer is Right**
The Galeazzi fracture is a classic example of a fracture of necessity, where a fracture of the radius is associated with a dislocation of the distal radioulnar joint. This dislocation is necessary to compensate for the instability caused by the radial fracture, which would otherwise lead to a non-union or malunion of the fracture. The distal radioulnar joint dislocation provides additional stability to the radius fracture, making it a fracture of necessity.

**Why Each Wrong Option is Incorrect**
**Option A:** Cotton's fracture is not a fracture of necessity, as it refers to a specific type of fracture involving the ulna and radius, but it does not require an associated injury for stability.

**Option D:** Rolando fracture is a type of fracture involving the base of the first metacarpal, but it is not typically described as a fracture of necessity.

**Clinical Pearl / High-Yield Fact**
When evaluating a fracture, it's essential to consider the associated injuries, as they can significantly impact the fracture's stability and treatment plan.

**✓ Correct Answer: B. Galeazzi fracture**