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.
mechanism of injury that causes talar dome fractures
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.
symptoms of a talar dome fracture
pain in the ankle, worse when ambulating or standing for long periods of time compared to periods where the patient is not doing much walking.
clicking type sensation in the ankle during ambulation.
locking of the ankle
sensation that the ankle is going to give out on them and they do not feel secure to bear weight on the ankle.
Swelling is a normal complaint in these conditions and the amount of swelling is usually proportional to the amount of activity one undertakes.
diagnosis of talar dome fracture
Diagnosis of these 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.
TREATMENT OF TALAR DOME FRACTURES
Treatments for this fracture are predicated on the severity of the defect along with the age and activity of the patient.
The simplest treatment is to place the patient in a cast to keep the ankle joint from moving and allowing the defect to heal. The patient may or may not be able to bear weight, at the discretion of the doctor.
Oral anti-inflammatory medication or pain medication may be prescribed to reduce the discomfort associated with this condition.
Once healing has occurred, physical therapy may be helpful to restore range of motion in the affected ankle joint. During this period and possibly beyond, the patient may wear an ankle brace to better stabilize the joint and hopefully prevent further injury.
In cases where the talar dome defect is too far into the joint and thus will never heal back on to the dome, surgical intervention may be necessary to remove the defect. Surgical treatment may involve a simple arthroscopic procedure to remove the bone chip to more complicated situations where there is open reduction where the ankle joint is opened, the talar defect is identified and put back into place and held there with internal fixation.
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 repositioning 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.