**Core Concept**
Tardy ulnar nerve palsy is a type of ulnar nerve dysfunction that occurs as a result of a chronic, repetitive mechanical stress on the nerve. This condition typically affects individuals who have a pre-existing condition, such as cubitus valgus (a condition where the elbow is bent outward), which leads to prolonged stretching of the ulnar nerve.

**Why the Correct Answer is Right**
The ulnar nerve is most commonly affected by cubitus valgus deformity, where the elbow is bent outward. This condition causes the ulnar nerve to be stretched over a longer distance, leading to chronic compression and eventual nerve damage. The compression of the ulnar nerve can lead to symptoms such as atrophy of the interosseous and hypothenar muscles, claw hand deformity, and sensory deficits in the fourth and fifth digits.

**Why Each Wrong Option is Incorrect**
**Option A:** This is not a valid option.
**Option B:** While cubitus valgus is a common cause of tardy ulnar nerve palsy, other conditions such as medial epicondylitis or direct trauma to the ulnar nerve can also lead to ulnar nerve dysfunction, but they are not the primary cause of tardy ulnar nerve palsy.
**Option D:** This option is not relevant to the pathophysiology of tardy ulnar nerve palsy.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize the association between cubitus valgus deformity and tardy ulnar nerve palsy, as early detection and treatment can prevent long-term nerve damage and improve patient outcomes.

**Correct Answer: C. Cubitus valgus deformity**