The patient was scanned 7 weeks after an inversion and rotational trauma of the ankle. The examination included assessment of the talocrural joint, peroneal tendons, subcutaneous tissues, fibula, talus, tibia, syndesmosis, anterior talofibular ligament, anterior tibiofibular ligament, and calcaneofibular ligament.
Ultrasound examination of the ankle demonstrates a moderate effusion of the talocrural joint. There is extensive subcutaneous edema in the ankle region.
The anterior talofibular ligament shows complete fiber disruption, consistent with a complete ATFL rupture. There is also a rupture pattern of the tibiofibular ligament at the level of the syndesmosis, indicating involvement of the stabilizing structures of the ankle mortise. In ligament injuries, ultrasound can demonstrate partial or complete fiber discontinuity; dynamic stress ultrasound may provide additional support for associated laxity.
A osseous avulsion fragment is visible distal to the fibula, probably related to a traction mechanism at the ligamentous insertion. The fragment measures approximately 5.09 × 9.43 mm. In this context, avulsion indicates ligamentous injury at the bony insertion, with an associated fracture fragment.
The position and contour of the talus appear abnormal compared with the expected sonographic appearance. However, ultrasound is limited for reliably assessing talar alignment, subtle mortise incongruity, or ankle fork instability.
The overall appearance is that of a severe ankle injury involving both the lateral ligament complex and the syndesmotic stabilizers, with associated joint effusion and soft tissue swelling.
1. Final diagnosis
Severe lateral ankle ligament injury with complete rupture of the anterior talofibular ligament, combined with syndesmotic ligament injury and a distal fibula fracture. There is moderate talocrural joint effusion and extensive subcutaneous edema.
2. Differential diagnosis
The most likely diagnosis is a high-grade lateral ankle sprain with complete ATFL rupture and associated syndesmotic injury. Additional considerations include distal tibial or fibular avulsion fracture, osteochondral injury of the talus, persistent syndesmotic instability, ankle mortise diastasis, or subtle talar subluxation. In the presence of persistent joint effusion, intra-articular cartilage or osteochondral injury should also be considered, as ultrasound has limited value for assessing these structures.
3. Teaching points
Ultrasound can reliably demonstrate superficial ligament injury, including partial or complete fiber disruption of the ATFL, and may identify associated soft tissue swelling, joint effusion, and avulsion fragments. Dynamic stress ultrasound can further support the presence of ligamentous laxity. However, ultrasound is limited for evaluating ankle mortise congruency, talar alignment, syndesmotic instability, and intra-articular osteochondral injury. When syndesmotic injury or malalignment is suspected, radiographs and, when indicated, CT or MRI are important complementary imaging modalities.
4. Injury/disease information
Combined lateral ligament rupture and syndesmotic injury is clinically relevant because it may compromise ankle mortise stability. A small avulsion fragment may indicate traction injury at a ligamentous insertion and should prompt careful assessment of bony alignment and joint congruency. Even when pain is relatively limited or sport has been resumed, syndesmotic instability or subtle talocrural incongruity may persist. Further imaging with ankle radiographs is advised, preferably including AP, mortise, and lateral views, and weight-bearing views when clinically feasible. If radiographs are abnormal or suspicion remains, referral to trauma surgery or orthopedics and additional CT or MRI should be considered. Until mortise instability and abnormal talar alignment have been excluded, contact sports, jumping, pivoting sports, and high-load activities should be avoided.
Marc is founder of, and trainer at, SonoSkills. SonoSkills is an organization dedicated to MSK ultrasound education. He's also an MSK Sonographer at EchoConsult in Roermond, the Netherlands.
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