Typically, in a young ‘normal’ individual, the Achilles tendon ruptures in the ‘critical zone’, a region of relative watershed hypovascularity 2-6cm proximal to insertion. Due to sports related trauma, especially squash and basketball, males are over-represented (M:F 5:1 – 6:1).

Predisposing condidions include: diabetes mellitus; systemic inflammatory illnesses (e.g. RA, SLE); repeated microtrauma; gout; use of fluoroquinolone antibiotics.

MRI appearances vary:
* partial-thickness tear shows high signal on long TR, and tendon swelling to >7mm AP
* full-thickness tear shows a tendinous gap filled with oedema or blood
* complete rupture shows retraction of tendon ends
When a plantaris muscle is present (as in this case) then it’s tendon is usually spared due to its more anterior insertion on the calcaneum.

For additional images of this case, as well as classification of Achilles tendon tears, please visit Radiopaedia.org here.
Reference: StatDx.com
Credit: Dr Frank Gaillard