**Core Concept**
Delayed complications of fractures refer to conditions that arise after the initial healing phase of a fracture. These complications can be due to various factors such as malunion, nonunion, or secondary to the fracture itself. The most common delayed complications include heterotopic ossification, complex regional pain syndrome, and avascular necrosis.

**Why the Correct Answer is Right**
The correct answer is determined by identifying which option does not belong to the category of delayed complications of fractures. Each option should be analyzed in the context of fracture management and complications. For instance, heterotopic ossification and complex regional pain syndrome are well-documented complications that occur after fractures.

**Why Each Wrong Option is Incorrect**
**Option A:** Heterotopic ossification is a known complication of fractures, particularly in the context of femoral neck fractures. It involves the formation of bone tissue outside the normal skeletal structure, leading to pain and limited mobility.

**Option B:** Nonunion is a recognized complication of fractures, especially in cases with inadequate immobilization, poor blood supply, or underlying medical conditions. It refers to the failure of the fracture to heal, resulting in persistent pain and instability.

**Option C:** Complex regional pain syndrome is a neuropathic pain condition that can occur after fractures, characterized by chronic pain, swelling, and limited range of motion. It is often associated with fractures of the upper limb.

**Option D:** Infection is not a delayed complication of fractures; rather, it is a potential complication that can occur at any stage of fracture management, from the initial injury to the post-operative period.

**Clinical Pearl / High-Yield Fact**
When managing fractures, it is essential to monitor for potential complications such as heterotopic ossification, nonunion, and complex regional pain syndrome. Early recognition and intervention can significantly improve patient outcomes.

**Correct Answer:** D. Infection