**Core Concept**
The most common complication of mid shaft humerus fracture is related to the proximity of the fracture site to the **radial nerve**. The **radial nerve** is a branch of the **brachial plexus** that runs through the **radial groove** of the humerus.

**Why the Correct Answer is Right**
The correct answer is related to the anatomical relationship between the **mid shaft humerus** and the **radial nerve**. The **radial nerve** is susceptible to injury due to its close proximity to the mid shaft of the humerus, making **radial nerve palsy** a common complication.

**Why Each Wrong Option is Incorrect**
**Option A:** Not specified, assuming it's not related to nerve injury.
**Option B:** Not specified, assuming it's not the most common complication.
**Option C:** Not specified, assuming it's not directly related to the **radial nerve**.
**Option D:** Not specified, assuming it's not the correct answer.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **radial nerve palsy** can result in **wrist drop** and **loss of extension** of the wrist and fingers.

**Correct Answer:** Radial nerve palsy.