The Utility of Tc-99m Hydroxymethylene Diphosphonate Single-photon Emission Computed Tomography/Computed Tomography in Symptomatic Os Trigonum.

Os trigonum is a congenital condition in which a bone ossicle fails to fuse to a secondary ossification center in the posterior aspect of the talar bone. Repetitive plantar flexion of the foot may elicit inflammation of the ossicles fibrous connective band, subsequently causing pain. It is common to misdiagnose os trigonum as an avulsion fracture. We report a case of a 23-year-old male with symptomatic os trigonum diagnosed on Tc-99m hydroxymethylene diphosphonate single-photon emission computed tomography-computed tomography (SPECT-CT). We also wish to emphasize on the use of SPECT/CT in not only allocating the ossicle anatomically but also for the purpose of evaluation an active source of pain in a region of multiple complex small bones.