**Core Concept**
Tardy ulnar nerve palsy is a late complication of cubitus valgus deformity, typically presenting years after a supracondylar fracture of the humerus in children. This condition is characterized by weakness and atrophy of the ulnar-innervated muscles due to delayed onset of ulnar nerve dysfunction.

**Why the Correct Answer is Right**
The ulnar nerve is susceptible to stretching and compression in cases of cubitus valgus deformity, leading to progressive nerve damage. As the child grows, the ulnar nerve is stretched by the progressive valgus deformity, resulting in delayed onset of nerve dysfunction, typically presenting in late childhood or early adulthood. This condition highlights the importance of proper treatment and management of supracondylar fractures in children to prevent long-term complications.

**Why Each Wrong Option is Incorrect**
* **Option A:** Tardy ulnar nerve palsy is not typically associated with radial head fractures.
* **Option B:** This condition is not a direct result of radial nerve damage.
* **Option C:** Medial epicondylitis, also known as golfer's elbow, is a separate clinical entity that affects the medial epicondyle, not the ulnar nerve.

**Clinical Pearl / High-Yield Fact**
Tardy ulnar nerve palsy is a classic example of a "delayed" or "late" complication of a childhood injury, emphasizing the importance of long-term follow-up and management of childhood fractures.

**Correct Answer:** C.