Which injury type did Glenn Cain sustain after falling from a tree?

Glenn Cain likely sustained a visible deformity to the forearm after falling from a tree, which indicates a significant injury, such as a fracture or severe soft tissue damage. When individuals fall from a height, the mechanism of injury often involves impact forces that can lead to broken bones, particularly in the forearm as it is commonly used to break a fall.

Visible deformities can manifest as abnormal angulation, displacement, or unusual positioning of the limb, all of which suggest a more serious injury compared to the other options. This visual cue is crucial in emergency assessments as it signifies that the injury may require immediate medical intervention, possibly including immobilization or surgical correction.

In contrast, other types of injuries listed might not present with the same level of urgency or immediate visible signs. For instance, while a fracture of the skull is a serious injury, it would likely present with other symptoms such as loss of consciousness or clear fluid drainage from the nose or ears, not just a visible deformity. Similarly, a sprain of the ankle typically involves soft tissue injury without visible deformities, and a concussion, while serious, is primarily a brain injury rather than a musculoskeletal one and doesn't cause visible changes in the affected area.