An Achilles tendon rupture is relatively easy to diagnose. Based on the history, it is often obvious that there is a rupture – this usually involves a sudden onset of pain; a feeling of the ankle giving way; simultaneous foot dorsiflexion and knee extension occurring as the mechanism; there may be an audible snap heard.
Clinically there may be a palpable gap in the tendon and being able to raise up onto the toes when standing on the injured side is either impossible or very difficult. Thompson’s test which is squeezing of the calf muscles when they are laying prone should result in foot plantarflexion. A ruptured Achilles tendon does not do this. Some even suggest the needle test for an Achilles tendon rupture.
Imaging with diagnostic ultrasound or an MRI are quite definitive at determining if a rupture is prssent.