Many causes can determinate a posterior ankle impingement and its diagnosis may be often difficult.

Sagittal T1 weighted (left) and Axial T2 weighted Mri scans (0,3 Tesla) of a professional football player with posterior ankle pain. 

The MR imaging shows a clear picture of synovial reaction between the bone and soft-tissue structures of the posterior ankle; a small os trigonum is noted, with a tenosynovitis of the flexor allucis longus tendon. The dynamic ultrasound exam allows to better discriminate the posterior impingement.