Symptoms of posterior ankle impingement. She has had 2 yrs worsening symptoms with limitation to Releve (ability to rise onto Pointe or Demi Pointe)...problematic in ballet. Outside XRs did not show Os Trigonum or Stieda process.  MRI is instrumental in identifying pathology. FHL synovial thickening without tendinosis.  Synovitis posterior subtalar recess. Large Os (red arrow) is obscured by stress related marrow edema and superimposed posterolateral synovial inflammation (white arrow).  Gr I sprain PTFL (blue arrow) which inserts onto Os.  Bright cleft at synchondrosis of Os (yellow arrow) indicates instability. 
There is no more physically demanding sport than ballet.  What case will you enter in the International Day of Radiology Sports Imaging Contest?