The mortise view of ankle shows a faint vertical lucency through the distal tibial epiphysis. There is also mild separation of the lateral malleolar growth plate.

The lateral ankle view shows presence of joint effusion.

The presence of possible Tillaux fracture (SH III fracture of distal tibial epiphysis) on plain x-ray was subsequently confirmed on CT scan of the ankle.

Tillaux fracture can be a very subtle finding and in adolescents presenting with ankle injury, careful inspection of the distal tibial epiphysis is needed.

Further reading –

http://www.emergucate.com/imaging-case-of-the-week-143-interpretation/

https://radiopaedia.org/articles/tillaux-fracture