**Core Concept**
Colles' fracture is an extra-articular fracture of the distal radius, typically occurring when a person falls onto an outstretched hand. The displacement of a Colles' fracture refers to the abnormal alignment of the bone fragments following the injury. Understanding the types of displacement is crucial for accurate diagnosis and treatment planning.

**Why the Correct Answer is Right**
The displacement of a Colles' fracture can be described in various ways, including dorsal angulation, radial shortening, and displacement of the distal fragment. Dorsal angulation refers to the tilting of the distal fragment towards the back, while radial shortening occurs when the distal fragment is displaced proximally, resulting in a shorter radius. These displacements are often assessed clinically and radiographically to determine the need for reduction and fixation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because dorsal angulation is a common displacement in Colles' fractures, often resulting from the force of the fall on the outstretched hand.
**Option B:** This option is incorrect because radial shortening is a recognized displacement in Colles' fractures, which can lead to decreased wrist mobility and function.
**Option C:** This option is incorrect because displacement of the distal fragment is a characteristic feature of Colles' fractures, often requiring reduction and fixation to restore normal anatomy.

**Clinical Pearl / High-Yield Fact**
When assessing a Colles' fracture, it is essential to evaluate the degree of displacement, particularly dorsal angulation, to determine the need for surgical intervention. A general rule of thumb is that fractures with more than 10-15 degrees of dorsal angulation may require reduction to prevent long-term wrist dysfunction.

**Correct Answer: D.**