12 - Cotton's fracture

*Trimalleolar ankle fracture is otherwise called as the Cotton's fracture.

*Trimalleolar fractures usually are caused by an abduction or external rotation injury. In addition to fractures of the medial malleolus and fibula, the posterior lip of the articular surface of the tibia is fractured and displaced, allowing posterior and lateral displacement and external rotation with supination of the foot.

*The medial malleolus may remain intact, with a tear of the deltoid ligament occurring instead of a malleolar fracture.

*Trimalleolar (cotton) fractures require open reduction more often than any other type of ankle fracture. The results of treatment of trimalleolar fractures usually are not as good as the results obtained for bimalleolar fractures.

*Indications for open reduction of the posterior malleolus or posterior tibial fragment depend chiefly on its size and displacement.

*If the fragment of the posterior malleolus involves more than 25% to 30% of the weight bearing surface, it should be anatomically reduced and held with internal fixation.
*If the fragment consists of less than 25% of the articular surface, it generally is of no consequence if the anterior part of the tibial articular surface is large enough to provide a stable weight bearing surface with which the talus can be held in proper relationship.

*Often, satisfactory reduction of the posterior tibial fragment occurs with anatomical and rigid fixation of the fibula because this fragment most often is posterolateral and attached to the fibula by the posterior tibiofibular ligament.

*If the posterior tibial fragment is small, even a proximally displaced position is of no consequence, but even the slightest posterior subluxation of the talus on the articular surface of the tibia is unacceptable.

*If there is a persistent step-off or gap of more than 2 to 3 mm or persistent posterior instability, open reduction is warranted.

*The posterior and proximal displacement of the tibial fragment creates an offset at the fracture. With the foot displaced posteriorly, this irregularity in the articular surface of the tibia is brought against the weight bearing surface of the talus, and with motion and weight bearing severe traumatic arthritis develops.

*In fractures with posterior malleolar fragments that constituted 25% or more of the joint, Observers found no clinical differences between fractures that were reduced and fixed and fractures that were not fixed. They noted that reduction of the posterior malleolar fragment generally was satisfactory when the lateral malleolar fracture was reduced and fixed. This reduction was well maintained, and late posterior subluxation of the talus did not occur with either method.