A medial malleolus fracture is a break in the tibia, at the inside of the lower leg. Fractures can occur at different levels of he medial malleolus.
Medial malleolar fractures often occur with a fracture of the fibula (lateral malleolus), a fracture of the back of the tibia (posterior malleolus), or with an injury to the ankle ligaments.
A posterior malleolus fracture is a fracture of the back of the tibia at the level of the ankle joint.
In most cases of posterior malleolus fracture, the lateral malleolus (fibula) is also broken. This is because it shares ligament attachments with the posterior malleolus. There can also be a fracture of the medial malleolus.
Depending on how large the broken piece is, the back of the ankle may be unstable. Some studies have shown that if the piece is bigger than 25% of the ankle joint, the ankle becomes unstable and should be treated with surgery.
It is important for a posterior malleolus fracture to be diagnosed and treated properly because of the risk for developing arthritis. The back of the tibia where the bone breaks is covered with cartilage. Cartilage is the smooth surface that lines a joint. If the broken piece of bone is larger than about 25% of your ankle, and is out of place more than a couple of millimeters, the cartilage surface will not heal properly and the surface of the joint will not be smooth. This uneven surface typically leads to increased and uneven pressure on the joint surface, which leads to cartilage damage and the development of arthritis.
“Bi” means two. “Bimalleolar” means that two of the three parts or malleoli of the ankle are broken. (Malleoli is plural for malleolus.)
In most cases of bimalleolar fracture, the lateral malleolus and the medial malleolus are broken and the ankle is not stable.
A “bimalleolar equivalent” fracture means that in addition to one of the malleoli being fractured, the ligaments on the inside (medial) side of the ankle are injured. Usually, this means that the fibula is broken along with injury to the medial ligaments, making the ankle unstable.
A stress test x-ray may be done to see whether the medial ligaments are injured.
Bimalleolar fractures or bimalleolar equivalent fractures are unstable fractures and can be associated with a dislocation.
“Tri” means three. Trimalleolar fractures means that all three malleoli of the ankle are broken. These are unstable injuries and they can be associated with a dislocation.
The syndesmosis joint is located between the tibia and fibula, and is held together by ligaments. A syndesmotic injury may be just to the ligament — this is also known as high ankle sprain. Depending on how unstable the ankle is, these injuries can be treated without surgery. However, these sprains take longer to heal than the normal ankle sprain.
In many cases, a syndesmotic injury includes both a ligament sprain and one or more fractures. These are unstable injuries and they do very poorly without surgical treatment.