In these cases, lesions may be due to osteonecrosis, endocrine disorders or genetic factors. Talar dome lesions do occur with no history of trauma. Contributing factors may include ligamentous laxity and recurrent ankle sprains. Talar dome fractures are directly related to ankle trauma. This explains why the cartilage at the site of a talar dome fracture can remain viable as the bone beneath it fails to heal. It's interesting to note that the cartilage of the ankle derives most of its nourishment from the fluid in the ankle joint, called synovial fluid, and not from the same blood supply that supplies the damaged bone. Aseptic (no infection) necrosis (death) of the talus is the single greatest influence that inhibits healing of talar dome fractures. The term aseptic necrosis is used to describe this type of an injury to the bone. In a talar dome fracture, the injury to the subchondral bone crushes the normal blood supply to the site of the injury. In severe cases, such as stages III and IV, the injured fragment of bone and cartilage becomes detached, creating even greater irregularities in the surface of the joint. Motion on this irregular surface creates pain and inflammation within the joint. As a result, the surface of the ankle joint becomes irregular. As the force of an injury is applied to the cartilage, the subchondral bone collapses in a localized fracture. This example is very similar to what happens in a transchondral talar dome fracture. The skin of the apple appears normal, yet the underlying supporting structure of the flesh of the apple is damaged. As an analogy, think of the injury sustained by an apple when it falls from a tree. ![]() "Across the cartilage" is actually a very accurate description of how transchondral fractures occur. The term transchondral refers to an injury applied to the bone across the cartilage. This mechanism of injury accounts for the fact that the 56.3% of talar dome fractures are found on the posterior medial aspect of the talar dome.(5) 43.7% of remaining transchondral fractures of the talus occur in the middle third of the lateral talar dome.(5) As the talus rocks out of position during the sprain, the position of the foot and ankle places the posterior medial aspect of the talar dome in a position where focused load is applied by the tibia to the talus as the body weight pushes down, compressing the ankle and talar dome. In an inversion sprain of the ankle, the typical position of the foot and ankle at the time of injury is with the foot inverted and the ankle slightly plantarflexed. The mechanism of injury of a talar dome fracture involves focused load in one specific spot of the talar dome. The talus is designed to carry load evenly distributed over the entire surface of the talus, thus decreasing load in any one particular spot. The Bristol classification was described by Hepple et.al. Stage IV - Focal compression of the subchondral bone with a fully detached fragment of cartilage, detached from the site of injury and floating in the joint space.Ī newer method of classification of transchondral talar dome fractures which uses MRI as the basis of classification is called the Bristol classification. Stage III - Focal compression of the subchondral bone with a fully detached fragment of cartilage, still situated in place at the site of injury Stage II - Focal compression of the subchondral bone with partial detachment of a fragment of cartilage Stage I - Focal compression of the subchondral bone (bone beneath the cartilage) Berndt and Hardy described four stages of transchondral fractures.īerndt and Harty Classification of Talar Dome Fractures: What Berndt and Hardy described was a classification of fractures found immediately beneath the surface of the cartilage of the talar dome. ![]() Injuries of the talar dome were first discussed in the medical literature by Kappis in 1922.(4) In 1959, Berndt and Harty were the first to recognize the unique nature of these injuries.(5) They called these injuries transchondral fractures. The talar dome is the rounded portion on the top of the talus that articulates with the bones of the leg (tibia and fibula.) This article discusses injuries of the talar dome. Injuries of the ankle joint can be complex and debilitating. These three unique bones work in conjunction to provide the range of motion necessary to complete our daily activities such as walking, jumping, or running. These three bones are the tibia, fibula, and talus. ![]() The human ankle is a complex, load-bearing joint that consists of just three bones.
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