44-year-old patient with an acute inversion injury of the right ankle two days previously. There was marked swelling and pain, with a reported VAS pain score of 7/10. Weight-bearing was painful and the Ottawa Ankle Rules were positive.
Ultrasound examination included assessment of the talocrural joint, peroneal tendons, distal fibula, talus, distal tibia, distal tibiofibular syndesmosis, anterior talofibular ligament (ATFL), anterior inferior tibiofibular ligament, calcaneofibular ligament (CFL), deltoid ligament, spring ligament, tarsal tunnel, posterior tibial tendon, flexor digitorum longus tendon, and flexor hallucis longus tendon.
There is discontinuity of the anterior talofibular ligament, consistent with a complete ATFL rupture.
The calcaneofibular ligament is thickened, oedematous, and hypoechoic. Fibre continuity is preserved, compatible with ligamentous sprain/strain without sonographic evidence of rupture.
The distal tibiofibular ligamentous complex demonstrates preserved continuity, without sonographic evidence of distal tibiofibular syndesmotic rupture.
There is medial peri-articular soft-tissue swelling. A small to moderate amount of intra-articular fluid is present within the talocrural joint.
1. Final diagnosis
Complete traumatic rupture of the anterior talofibular ligament following an inversion injury, associated with sprain/strain of the calcaneofibular ligament without demonstrable CFL rupture. No sonographic evidence of rupture of the distal tibiofibular syndesmosis. Associated reactive peri-articular soft-tissue swelling and small to moderate talocrural joint effusion.
2. Differential diagnosis
Given the marked pain, painful weight-bearing, and positive Ottawa Ankle Rules, an associated traumatic osseous injury should be excluded. Ultrasound is not the appropriate imaging modality for reliably excluding an ankle fracture.
3. Teaching points
Acute inversion injuries most commonly affect the lateral ligament complex, with the ATFL being particularly vulnerable. Ultrasound can demonstrate ligament discontinuity in complete ATFL rupture and can differentiate this from a thickened, hypoechoic but continuous ligament in a lower-grade CFL injury. Assessment of the distal tibiofibular syndesmosis is important because associated syndesmotic injury may substantially alter injury severity and management. When the Ottawa Ankle Rules are positive, radiographic assessment remains indicated irrespective of the ultrasound findings.
4. Injury/disease information
A complete ATFL rupture represents a high-grade lateral ankle ligament injury and may occur together with injury to the CFL. In the absence of an associated fracture, lateral ankle ligament injuries are commonly managed initially with functional protection, progressive weight-bearing according to symptoms, and subsequent rehabilitation focusing on mobility, strength, proprioception, and restoration of ankle stability. Persistent severe pain, instability, or an atypical clinical recovery may warrant reassessment and additional imaging such as MRI. In this case, ankle radiographs are recommended according to the Ottawa Ankle Rules to exclude an associated fracture.
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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