The left ankle x-rays show Tillaux fracture which is a Salter Harris type III fracture of the distal tibia. The fracture is very subtle. Key is identifying the ankle joint effusion which should alert one to the possibility of an occult fracture.

The AP ankle x-ray shows a subtle lucency traversing the distal tibial articular surface with widening of the lateral growth plate.

The lateral ankle view shows obliteration of the Kager’s triangle and ankle tear drop sign, indicating ankle joint effusion, which in the context of trauma will mean a haemarthrosis. There is also a step on the anterior aspect of the distal tibia at the fracture site.

This patient was managed conservatively with leg immobilisation and non weight bearing.

Tillaux fracture:

• Accounts for 3-5 % of paediatric ankle fractures.
• Age group 12-14 years.
• Mechanism is supination external rotation of the ankle.
• Salter Harris III fracture of the anterolateral distal tibial epiphysis.
• Treatment – non operative with closed reduction and casting if < 2mm separation.                  – operative if more than 2mm separation after reduction attempt.

Reference :https://www.orthobullets.com/pediatrics/4028/tillaux-fractures