**Core Concept**
Injury due to fall on outstretched hand in elderly individuals is often associated with osteoporosis and fragility fractures. The mechanism of injury involves a fall onto a flexed wrist, leading to compression of the distal radius.

**Why the Correct Answer is Right**
The most common injury sustained due to this type of fall is a Colles' fracture, which is a type of distal radial fracture. This occurs due to the compression force on the distal radius, resulting in a fracture through the metaphysis of the bone. The distal radius is particularly susceptible to fractures in elderly individuals due to osteoporosis, which reduces bone density and increases the risk of fractures.

**Why Each Wrong Option is Incorrect**
**Option A:** Scaphoid fracture is a common injury, but it is not the most common injury in this scenario. Scaphoid fractures typically occur due to a fall onto a flexed wrist, but they are more common in younger individuals.
**Option B:** Radial head fracture can occur due to a fall onto a flexed elbow, but it is not the most common injury in this scenario. Radial head fractures are often associated with a different mechanism of injury.
**Option C:** Distal ulnar fracture can occur due to a fall onto a flexed wrist, but it is not the most common injury in this scenario. Distal ulnar fractures are less common than Colles' fractures in this context.

**Clinical Pearl / High-Yield Fact**
In elderly individuals, falls onto an outstretched hand are a common mechanism of injury for distal radial fractures. Osteoporosis and reduced bone density increase the risk of fractures in this population. A thorough history and physical examination should be performed to assess for other injuries and underlying conditions.

**Correct Answer:** C. Distal radial fracture.