Normal Achilles Tendon Evaluation
The patient should be placed in a prone position so that you can easily reach the area of interest. The high frequency linear probe is placed in a longitudinal plane along the posterior ankle with the probe indicator toward the patient's head. The Achilles tendon may be visualized as a hyperechoic straited area (below pic). Moving from the proximal calf to the heel, the tendon may be followed to its insertion at the calcaneus.
Achilles Tendon Rupture
The Achilles Tendon attaches the soleus and gastrocenemius muscles to the calcaneus. Rupture is due to forceful plantar flexion. If there is a full thickness tear, as in this case, there will be a complete disruption of the tendon fibers with resultant retraction of the tendon proximally. This usually occurs about 3-4 cm proximal to the attachment to the calcaneus where there is a decreased vascularity. The ends of the ruptured tendon usually appear tapered and may cause some acoustic shadowing posteriorly (refraction). The space between the two tendon stumps may be filled with heterogeneous fluid, anechoic fluid (blood) or some of the adjacent fatty tissue (from Kager's fat pad).
It is important to evaluate the tendon in motion. This can be done by calf squeeze or by passive motion of the foot. This will make a tendon tear more obvious as one of the tendon stumps will move but the other will not.
Lastly, watch for an avulsion fracture of the calcaneus in Diabetic patients, which can mimic an Achilles tendon tear. The tendon itself will remain intact, but the portion of the calcaneous where the tendon attaches will be fractured off. This will be evident as you follow the tendon distally to the calcaneus.
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