## Core Concept
Tardy ulnar nerve palsy refers to a delayed onset ulnar nerve dysfunction, often resulting from a childhood injury that leads to progressive deformity and nerve damage over time. This condition typically arises due to deformities or malunions that put the ulnar nerve under chronic stress or damage.

## Why the Correct Answer is Right
The correct answer, **b) Lateral condylar #**, is associated with tardy ulnar nerve palsy. A lateral condylar fracture of the humerus in children can lead to a cubitus valgus deformity if not properly aligned during healing. Over time, this deformity can cause stretching or damage to the ulnar nerve, leading to tardy ulnar nerve palsy. The mechanism involves progressive valgus deformity that increases tension on the ulnar nerve, particularly as the child grows.

## Why Each Wrong Option is Incorrect
- **Option A: Supracondylar #** - While supracondylar fractures are common in children and can lead to nerve injuries, they are more commonly associated with immediate nerve damage rather than tardy ulnar nerve palsy.
- **Option C: Olecranon #** - Olecranon fractures can directly damage the ulnar nerve but are not typically associated with the progressive deformity leading to tardy ulnar nerve palsy.
- **Option D: Intercondylar #** - Intercondylar fractures can be complex and involve various structures around the elbow but are less commonly linked to the specific mechanism of tardy ulnar nerve palsy compared to lateral condylar fractures.
- **Option E: Distal radio-ulnar dislocation** - This injury would more likely affect the distal radioulnar joint and is not commonly associated with ulnar nerve palsy.

## Clinical Pearl / High-Yield Fact
A key point to remember is that tardy ulnar nerve palsy often presents years after the initial injury, making it crucial to consider a patient's past medical and trauma history when diagnosing ulnar nerve dysfunction. Cubitus valgus deformity following a lateral condylar fracture is a classic predisposing factor.

## Correct Answer: B. lateral condylar #