What is the most accurate test to confirm a complete Achilles tendon rupture in a patient with sudden calf pain?

To confirm a complete Achilles tendon rupture, the most accurate test is the observation of no plantar flexion on calf flexion, also known as the Thompson test. This clinical examination involves squeezing the calf muscle while the patient is in a prone position; if the Achilles tendon is intact, this maneuver will result in plantar flexion of the foot. Conversely, if the tendon is ruptured, there will be no movement, indicating a complete loss of function.

This is an effective, quick, and non-invasive way to assess the integrity of the Achilles tendon and is commonly performed in clinical settings. While ultrasound and MRI can provide imaging confirmation of a rupture, the Thompson test directly evaluates the functional ability of the tendon and is widely regarded as a reliable clinical indicator in acute settings.

In this context, the other options, while they may have their uses, do not provide the same level of immediate functional assessment or accuracy in confirming the diagnosis of a complete Achilles tendon rupture.