One of the bones comprising the ankle is the talus bone which forms part of the foot. It forms the “floor” of the ankle joint. It derives the name "dome" because it sits cradled on top of the calcaneus with the top portion of the bone forming a dome like structure to allow for the up and down motion of the foot. Ligaments attach the talus bone to the tibia and fibula bones to complete the ankle joint.
In a severe ankle sprain, usually the medial and lateral ankle ligaments bear the brunt of the trauma, but sometimes the sprain may be so severe that the talus bone is displaced resulting in trauma to the bone and in many cases may be severe enough to cause a fracture within the talus.
In the majority of cases there is a severe inversion sprain along with a resulting dorsiflexion of the foot (the ankle turns inward and at the same time the foot is jerked upwards). Usually the top or dome is affected and thus we end up with a fracture of the dome. The incidence of this type of fracture in ankle sprains is estimated to be in the range of 2-6%. Since the talar dome is made of cartilage (which is what allows the foot to bend up and down smoothly) if it does not heal properly a small piece of cartilage may actually break off creating a defect in the otherwise smooth pearly nature of cartilage. The broken piece of cartilage may then “float” in the ankle joint acting as a foreign body which can be irritating to the joint and cause pain.
Diagnosis of talar dome fractures can be difficult to make as it is quite often overlooked when a patient complains of ankle pain particularly if the ankle sprain was not considered serious.
An xray would be the first diagnostic test performed and often it is a good idea to take the same views of the other ankle for comparison purposes. If an xray proves to be uneventful and your doctor suspects a talar dome fracture, an MRI or CT scan may have to be performed for a more definitive view of the talus.
Once in a while, a local anesthetic may be injected directly into the joint, in an effort to see if the pain is coming from deep in the joint. If relief occurs, it may indicate the possibility of a talar dome fracture. It should be noted for clarification purposes that these type of talar dome fractures that create a loose body of cartilage are also known as an osteochondral defect.
Treatments for this fracture are predicated on the severity of the defect along with the age and activity of the patient.
The problem with a talar dome fracture, particularly one that does not heal properly is that it further inflames the joint causing more damage to the ankle joint resulting in a more arthritic ankle. This situation could result in further pain, more limitation of motion in the joint and chronic swelling. One of the complications of improper removal or poor re-positioning of the talar defect is that the bone chip may undergo avascular necrosis which means the bone chip actually dies due to lack of circulation and most certainly will then act as an irritant within the joint.