Common injuries of the Leg, Knee, Ankle, and Foot

Discuss common injuries of the Leg, Knee, Ankle, and Foot. List the body part, then name and describe (what part of the body is injured) at least ONE injury for each and HOW it occurs (10pts per body part and injury). You may identify more than one injury for each if you wish. ;-)
Example:

Ankle: (body part) Ankle sprain (NAME of injury). A sprain occurs when the ankle is forced to move out of its normal position causing one or more of the ankle's ligaments to stretch, partially tear or tear completely (what body PART is injured). Injury can occur when participating in sports, walking on uneven surfaces, or even wearing inappropriate footwear (cause or HOW injury occurs).