**Core Concept:** Elbow Valgus Deformity, Ulnar Nerve Compression, Post-traumatic Fracture Healing

A 6-year-old girl presents with a progressive valgus deformity of the right elbow since 2 years, along with tingling in ulnar one and a half fingers. She had a history of a cast applied for 6 weeks following a fall on an outstretched hand 2 years back.

**Why the Correct Answer is Right:**

The correct answer is **D** because the patient's clinical presentation aligns with the scenario of a post-traumatic ulnar nerve compression secondary to an elbow valgus deformity. The valgus deformity and tingling symptoms in ulnar one and a half fingers are indicative of ulnar nerve compression. The history of a cast applied for 6 weeks following a fall on an outstretched hand 2 years back further supports the diagnosis as it could have led to ulnar nerve compression during the healing process.

**Why Other Options are Incorrect:**

Option A (epicondylitis) and Option B (epicondylitis) are incorrect because they relate to conditions affecting the medial and lateral epicondyles, respectively, rather than the ulnar nerve. Epicondylitis is an inflammation of the tendons inserting on the epicondyles, causing pain and limited range of motion, but does not involve ulnar nerve compression.

Option C (epicondylitis) is incorrect for the same reasons as Option A.

**Clinical Pearl:**

In cases of post-traumatic elbow deformities, it is essential to consider the possibility of ulnar nerve compression, especially when there is a history of trauma and subsequent immobilization. This is especially crucial in pediatric cases, where the immobilization period may be longer due to the child's growth and development. Timely diagnosis and treatment can prevent long-term complications related to nerve compression, such as ulnar nerve palsy or cubital tunnel syndrome.