Anatomy and Pathology of the Achilles Tendon Tracy MacNair Achilles • Achilles was the warrior and hero of Homer’s Iliad • Thetis, Achilles’ mother, made him invulnerable to physical harm by immersing him in the river Styx after learning of a prophecy that Achilles would die in battle • The heel she held him by remained untouched by water and vulnerable • Achilles led the Greek military forces, which captured and destroyed Troy after killing the Trojan Prince, Hector • Hector’s brother Paris killed Achilles by firing a poisoned arrow into his heel Outline • Anatomy • Pathology o General anatomy o Clinical findings o Gastrocnemius muscle o Peritendinitis o Soleus muscle o Paratendinitis o Achilles tendon o Partial & Complete tears o Calcaneal tuberosity o Muscle atrophy o Blood supply o Osseous abnormalities o Retrocalcaneal bursa o Insertional pathology o Peritenon o Myotendinous junction o Plantaris o Retrocalcaneal bursitis o Surrounding soft tissues o Haglands deformity • Biomechanics o Xanthoma • Epidemiology • Post surgical imaging General Anatomy • Achilles tendon is the strongest + largest tendon in the body • Formed by conjoined tendons of gastrocnemius and soleus muscles (triceps surae) • Gastrocnemius muscle (GM), soleus muscle (SM), Achilles tendon (AT) and plantaris located in posterior, superficial compartment Gastrocnemius Anatomy • Fusiform, biarticular muscle • High proportion of fast-twitch type II muscle fibers (rapid movement) • Medial head (MG) larger; originates from popliteal surface of femur just superior to MFC • Lateral head (LG) originates from posterolateral surface of LFC and lateral lip of the linea aspera • Two muscle bellies extend to middle of the calf where they join • Tendon forms on deep surface • Tendon 10-15 cm in length Soleus Anatomy • Multi-pennate monoarticular muscle • Immediately deep to GM • Predominantly slow-twitch type I muscle fibers with high fatigue resistance (postural muscle) • Arises from posterior head and proximal 1/4 of fibular shaft, soleal line and from fibrous band between the tibia and fibula Soleus Anatomy • Muscular fibers terminate in a broad aponeurosis on the posterior surface • Gastrocnemius and soleus aponeuroses parallel each other for variable distance before uniting • Large variation in soleus musculotendinous junction • ? cut off for low lying soleus o Pichler et al. Anatomic Variations of the Musculotendinous Junction of the Soleus Muscle and Its Clinical Implications. Clinical Anatomy 2007; 20:444–447. Low Union of Gastrocnemius and Soleus Tendons • Gastrocnemius and Soleus tendons may remain separate up to their calcaneal insertions • Can mimic tendinosis on axial images and a longitudinal tear on sagittal images • Increased SI smooth + linear • Gradual tapering on sagittal images • Rosenberg ZS et al. Low incorporation of soleus tendon: a potential diagnostic pitfall on MR imaging. Skeletal Radiol (1998) 27:222±224 Accessory Soleus • Rare congenital anatomical variant (0.7%) • Arises from anterior surface of the soleus, soleal line of the tibia or proximal fibula • Inserts as muscle or tendon onto medial surface of calcaneus or into Achilles' tendon • Separate blood supply from posterior tibial artery and separate fascial sleeve • Manifests in late teens because of muscle hypertrophy due to increased physical activity • Majority present with a painful swelling caused by muscle ischemia or a compressive neuropathy involving the posterior tibial nerve Achilles Anatomy • Begins at junction of gastrocnemius and soleus tendons in middle of calf • Contribution of gastrocnemius and soleus tendons varies • Typically 3 to 11 cm in length • Rotational twist before inserting on calcaneus o gastrocnemius fibers insert laterally o soleus fibers insert medially