Figure 1. 17-year-old male ballet dancer. (a) Sagittal spin echo T1 weighted MR (TR/TE, 722/20) image demonstrating an os trigonum posterior to the talus, between the posterior plafond of the tibia and the calcanium. Excess soft tissue (arrow) indicating a synovitis is seen in this interval. (b) Sagittal short tau inversion recovery (TR/TE/TI, 4655/30/130) demonstrates high signal within the os trigonum and the talus (arrows).