Syndesmotic Injuries of the Ankle

Syndesmotic Injuries of the Ankle

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. If the incisura is shallow, the fibula can be pushed anteriorly. If the incisura is deep, then the fibula can be pushed posteriorly, and this can cause malreductions and malrotation. Syndesmotic malreduction can occur from positioning of the reduction clamps. Anterior clamps can cause malreduction. Avoid translation of the fibula anteriorly when using anteriorly based clamps. Clamp placement in a neutral anatomical axis reduces syndesmotic malreduction. While oblique placed clamps results in syndesmotic malreduction, variation in the angulation of the reduction clamp and screw placement can cause iatrogenic syndesmotic malreduction and displaces the fibula in external rotation. Fixation of the fibula in as much as 30 degrees of external rotation may go undetected using intraoperative fluoroscopy. The malreduction may not be clinically significant if it is minimal; however, it can be very significant if the malreduction is significant. Screw fixation is supposed to be the gold standard for syndesmotic fixation; however, this is no longer the gold standard fixation method. You can fix the syndesmosis by screws, by suture buttons, and by a variety of different techniques. Patients with suture buttons return to work early and less frequently need their implant removed. The controversy is that there is no gold standard for the number of screws used, the number of cortices, the level of placement of the screws, the type of screws (3.5 or 4.5). I personally use 3.5 screws and rarely use 4.5 screws. I may also use cross screws in severe situations. I also use a plate in Maisonneuve fractures, not just screws over the fibula, the screws have to go through a plate to help the stability of the screws. You must have anatomic reduction of the fibula, as well as alignment. Achieving the fibular length can be a problem, especially if the fibula is comminuted. In this situation, you need to fix the medial malleolus first, then restore the fibular length.

The Dime Sign, the Shenton’s line, and the uninterrupted subcortical line. Syndesmotic screws are rigid, and they can break or loosen. The tight rope fixation avoids the problem of the rigid fixation, so it maintains the reduction while allowing physiological movement of the fibula (tight rope fixation has its own problems). I used to remove all syndesmotic screws, but now I don’t remove them unless it is necessary for pain or stiffness. I make the patient walk on it around 10-12 weeks. 17% of the screws will break, 13% become loosened, and ¼% of the screws are removed due to symptoms. The screws look bad on x-rays when they are broken or loosened, but these screws don’t cause a lot of trouble. If you keep the screws, it is just an x-ray problem and not a functional problem. If you leave the screws or if you remove the screws, there is no difference in functional outcome between screw removal and nonremoval. They found that when the syndesmosis is malreduced and then you remove the screws, then the patient feels better and the movement gets better. Retained, broken screws had a better functional outcome than the retained, intact screws. Fixation of the posterior malleolus adequately stabilizes the syndesmosis. If the fragment is minimally displaced, then the screws can be directed anteriorly to posteriorly. If the fragment is large, you can fix it with a buttress plate posteriorly. The posterior malleolar fixation restores the stiffness to 70% and the syndesmotic screw fixation restores the stiffness to 40% compared to intact specimens. There is a strong association between obesity and loss of syndesmotic reduction. Obese patients are 12 times more likely to lose syndesmotic reduction than nonobese patients. In regards to the syndesmotic injury, you will need to recognize it and fix it when the syndesmosis is unstable. Evaluate the reduction of the syndesmosis. Avoid malreduction. Remove syndesmotic screws only if needed.