MR imaging of disorders of the Achilles tendon.

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he Achilles tendon is among the most frequently injured tendons of the body with a variety of types of traumatic and overuse conditions affecting it. These conditions are common, often come to clinical attention, and are frequently imaged. The pathophysiology of Achilles disorders is complex, and the nomenclature is irregularly applied; this leads to miscommunication between clinicians and radiologists and inconsistencies in the literature. Therefore, we review the anatomy, MR imaging findings, and pathologic findings in an attempt to develop a systematic nomenclature. Gross Anatomy The Achilles tendon originates in the mid leg and is formed by the junction of the two heads of the gastrocnemius muscles and the soleus muscle [1, 2]. The bulk of the Achilles is formed from the gastrocnemius muscle. The larger medial head originates almost entirely from just proximal to the medial femoral condyle, and the smaller lateral head arises from both the posterior and lateral surfaces of the lateral femoral condyle. At the junction of the proximal and mid calf, the two heads of the gastrocnemius muscles and their tendons approximate midline. The gastrocnemius tendon origin is gradual, occurring over approximately 3‐4 cm. The fibers of the medial head originate slightly lower than those of the lateral head. The Achilles tendon is not formed until the soleus muscle inserts onto the gastrocnemius tendon, approximately 3‐4 cm more distally [2]. The plantaris muscle originates from the lateral meniscus and the lateral femoral epicondyle in close association with the lateral head of the gastrocnemius muscle. The plantaris tendon then crosses obliquely between the soleus and gastrocnemius muscles and continues just medial to the Achilles. Various plantaris insertions are seen, but most fibers insert on the medial aspect of the superior calcaneal tuberosity or 1 cm anterior and medial to the Achilles on the calcaneus, a distinct insertion point separate from that of the Achilles. The Achilles‐plantaris complex is termed the “triceps‐surae complex” [3].