Dr. Ebraheim’s educational animated video describes syndesmotic injury of the ankle.
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The syndesmosis gives stability to the ankle. It resists external rotation and axial and lateral displacement of the talus. Syndesmotic injuries of the ankle can be challenging in the diagnosis and in the treatment. It may not be easy to obtain and maintain reduction of the syndesmosis. Approximately 50% of the patients with operatively treated supination/external rotation type fracture of the ankle have syndesmotic injury on stress radiographs intraoperatively. Anatomic reduction of the syndesmosis is crucial for a good clinical outcome. Restoration of the normal fibular length and alignment, as well as obtaining and maintaining the alignment of the syndesmosis significantly impacts the functional outcome of the patient. Malreductions of the tibiofibular syndesmosis is not uncommon, and it can occur in up to 30% of the patients. Fluoroscopy, direct visualization and reduction of the syndesmosis could improve the anatomic reduction. Syndesmotic injuries are common. They are found in sports injuries (high ankle sprain) or in ankle fractures such as supination/ external rotation Type IV, pronation/ external rotation and pronation/ abduction injuries. It does not occur with supination/adduction injury. In this injury, you will see vertical fracture of the medial malleolus and the talus will go medially. Syndesmotic fixation probably is needed more with an ankle fracture that has a high fibular fracture and deltoid ligament injury, than an ankle fracture that has fracture of the fibula with medial malleolus fracture. The higher the fracture in the fibula, the more incidence of syndesmotic disruption and the need for syndesmotic fixation. In fact, the high fibular fracture plus deltoid injury equals syndesmotic screw fixation (means syndesmotic screw fixation is needed more). To diagnose a syndesmotic injury, you will find an unstable mortise; it can be evident or occult. You also need to suspect syndesmotic injury in proximal fibular fracture, which is called Maisonneuve fracture. Look at the disruption of the interosseous membrane and the syndesmosis. You do this by looking at the ankle and get an x-ray. You also suspect syndesmotic injury with sports injuries where there is a positive squeeze test (high ankle sprain). 20% of syndesmotic injuries of the ankle can be undetected on clinical examination. You should get stress-rays. You also suspect it in supination/external rotation Type II injury that has a fibular fracture. Provocative tests or the stress views are used in fibular fractures supination/external rotation Type II to see if it is really a Type II injury or if the injury is a Type IV and there is a hidden occult deltoid and syndesmotic injury. To do the provocative tests to diagnose an occult injury or syndesmotic injury of the ankle, do the gravity test or do the abduction/external rotation stress views or do weight bearing film. In weight bearing films, the dorsiflexion of the ankle can eliminate any errors on the medial side. Sometimes when the ankle is plantar flexed, the medial side looks widened, but it is not a true widening. Look for the tibiofibular clear space, look for the tibiofibular overlap, and look for the widened medial clear space (more than 5mm). The tibiofibular clear space will be greater than 5mm with syndesmotic injury. The tibiofibular clear space is probably the best radiologic measure because it is not affected by the position of the leg. If the syndesmosis is unstable, you need to fix it. It is the last part of ankle fracture fixation. You must have anatomic reduction of the syndesmosis. Before you fix the syndesmosis, you will need to evaluate the reduction of the syndesmosis. This can be done by direct inspection and reduction or by x-rays. You may need x-rays of the other side to assess accuracy of reduction of the syndesmosis intraoperatively. In surgery, you can test the stability of the syndesmosis. You can use the cotton test, use a bone hook, or pull on the fibula by levering it out by hemostat, by a freer or an elevator, or you can see the movement of the fibula. You can also do the abduction/external rotation test. You will do x-ray intraoperatively and check if the syndesmosis is stable or not and if it is reduced or not. So you want to restore the fibular length and see if the medial clear space and tibiofibular overlap are OK or not. Make sure that you do not have mortise instability, which is displacement of the talus out of the mortise. You want to restore the fibular length because this is key. The fibula must sit properly in the incisura. The morphology of the incisura is variable and that encourages malreduction.