SPECT/CT for Discrimination Between Active and Inactive Os Trigonum in Posterior Ankle Syndrome

[^99mTc]-3,3-diphosphono-1,2-propanodicarboxylic acid bone scintigraphy was used to differentiate between posterior impingement syndrome and Haglund syndrome in a 34-y-old man with unclear right-sided ankle pain. The patient had an accessory os trigonum bilaterally, and previous x-ray, MRI, and CT were inconclusive. Using SPECT/CT with new iterative reconstruction algorithms based on CT images, the pathologic activation of bone metabolism at the right-sided os trigonum and the adjacent talus joint was revealed. Other causes of posterior ankle pain were ruled out, and posterior impingement syndrome was diagnosed.