Final answer:
Posterior malleolar fractures are associated with 'high ankle sprains,' which affect the stability of the ankle joint and are considered unstable.
Step-by-step explanation:
Posterior malleolar fractures are associated with syndesmotic ankle sprains, commonly referred to as "high ankle sprains," and are considered to be unstable. Such fractures involve the rear portion of the ankle and can be highly problematic because they affect the stability of the ankle joint. The posterior malleolus is part of the tibia that forms the back of the ankle and when fractured, it can compromise the syndesmosis which is the connection between the tibia and fibula, thereby destabilizing the ankle.
The syndesmosis is a fibrous joint where the tibia and fibula are held together by ligaments and the interosseous membrane. Injury to this area, especially with a fracture of the posterior malleolus, requires prompt medical attention to ensure proper healing and prevent long-term complications.