**Core Concept:** Fracture shaft humerus refers to a fracture occurring in the middle third of the humerus bone, which is the long bone in the upper limb connecting the shoulder joint to the elbow joint. The complications can be both non-operative and operative, depending on the severity and patient factors.

**Why the Correct Answer is Right:** The correct answer (C) is related to an operative complication, which is compartment syndrome. This occurs when a fracture causes the muscles and tissues in a specific compartment of the arm to swell, leading to increased pressure and impaired blood flow. If not addressed promptly, compartment syndrome can lead to tissue necrosis, muscle damage, and potential loss of the limb. Immediate surgery is required to relieve the pressure and restore blood flow, preventing severe complications.

**Why Each Wrong Option is Incorrect:**

A. Non-operative complications (e.g., malunion, non-union, or deep infection) do not require immediate surgery unless they progress to severe complications.
B. The type of fracture (e.g., simple or unstable) does not dictate immediate surgery unless the fracture is unstable and at risk of displacement or malreduction.
D. The presence of a fracture does not inherently require immediate surgery, but rather the severity of the associated complications dictates surgical intervention.

**Why Option C is Right:**

Option C refers to compartment syndrome, a life-threatening condition that necessitates immediate surgical intervention. This is a high-yield point to remember, as it showcases the importance of early recognition and management of severe complications following a fracture.

**Clinical Pearl:** In cases of suspected compartment syndrome following a fracture, it is essential to promptly consult with a surgeon and consider emergent surgery to prevent severe tissue damage and potential limb loss.