In all the above-described mimics, it is crucial to evaluate older images. Additionally, when in doubt, it is useful to consult a book of reference describing the normal variations of the skeletal system (e.g. Keats, T.E.; Atlas of Normal Roentgen Variants That May Simulate Disease). Each Emergency Assistance department should have such a (thick!)reference book.
Figure 9. Lateral ankle image with an accessory ossification center dorsal from the talus; the os trigonum.