**Core Concept:**
Colle's fracture is a type of metaphyseal fracture of the distal radius, often seen in children and young adults. It is characterized by a spiral or oblique fracture of the distal radius, resulting in a dorsal angulation and volar tilt of the distal fragment. The fracture line runs through the radial styloid process, which can lead to complications if not appropriately treated.

**Why the Correct Answer is Right:**
The correct answer is "D. Colles' fracture non-union." A non-union is a condition where the fracture fails to heal despite adequate treatment, leading to persistent pain, limited range of motion, and possible deformity. In the case of a Colles' fracture, a non-union can occur due to the unique fracture pattern involving the radial styloid process and metaphyseal and epiphyseal regions. Delayed or improper treatment can lead to this complication.

**Why Each Wrong Option is Incorrect:**

A. Mallet Fracture: This is a different fracture pattern involving the distal radius, usually associated with a closed injury. The mallet fracture is characterized by fracture lines in the radial and ulnar cortices of the distal radius, while Colles' fracture involves the radial styloid process and metaphyseal and epiphyseal regions.

B. Flexor Pollicis Longus Tendon Avulsion: This complication is related to the flexor pollicis longus tendon avulsion from the base of the fifth metacarpal. It is a different complication than a non-union in Colles' fracture.

C. Volar Plate Avulsion: The volar plate is a part of the collateral ligaments, which stabilize the distal radioulnar joint. An avulsion of the volar plate is a different complication than a non-union in Colles' fracture.

**Clinical Pearl:**
In cases of Colles' fracture, it is essential to assess for and promptly treat any associated soft tissue injuries or avulsion injuries to prevent complications like non-union. Appropriate management, including immobilization, splinting, and physiotherapy, can help achieve a successful union of the fracture fragments and prevent non-union. In cases of non-union, further intervention may be necessary, such as bone grafting or surgical fixation, depending on the severity of the non-union and the patient's condition.