Conditions of the Ankle Quiz

See Ankle Fracture. Option D is correct because a bimalleolar fracture means the medial malleolus and the lateral malleolus are both broken. A malleolus is a bony bump at the ankle: the medial malleolus is the lower end of the tibia (the shin bone) on the inner side, and the lateral malleolus is the lower end of the fibula (the thinner outer bone) on the outer side. Together they form a fork, the ankle mortise, that grips the talus (the bone that sits between them, above the heel bone). Fractures usually involve more than one malleolus, because a force applied in one direction often damages the ligaments on the other side of the ankle as the talus shifts, and these ligaments can pull a piece of bone off where they attach. The ankle behaves like a ring, so if it is broken in one place it is often damaged in another. A simple counting rule works: bi means two malleoli, tri means three, with the third being the posterior malleolus, the back edge of the tibia. The terms to know are:

• Bimalleolar: medial and lateral malleoli
• Trimalleolar: medial, lateral and posterior malleoli
• Bimalleolar-equivalent: lateral malleolus fracture plus a torn deltoid ligament (the strong ligament on the inner side)

• Bimalleolar fracture: both the medial and lateral malleoli are broken.
• Medial malleolus: the lower end of the tibia on the inner side.
• Lateral malleolus: the lower end of the fibula on the outer side.