The Achilles tendon (Fig. 47) represents the conjoined tendon of the gastrocnemius and soleus muscles, and may have a small contribution from the plantaris . Located in the superficial, posterior compartment of the calf, the Achilles tendon is subjected to the highest loads of any tendon in the body . Plantarflexion during running or jumping may subject the tendon to loads up to 10 times body weight . Chronic degeneration of the Achilles tendon is an overuse syndrome thought to be a result of repetitive microtrauma . Some authors suggest that local inflammation contributes to pain from Achilles tendinosis, although tendon biopsies show an absence of inflammatory cell infiltration and normal prostaglandin levels in degenerated tendons . Quantitative radioisotope studies have demonstrated that in the middle portion of the tendon (3 to 6 cm proximal to insertion), the intravascular volume is decreased compared with the remainder of the tendon , suggesting that decreased blood supply may be a contributing factor to development of tendon degeneration. However, Doppler evaluation of microvasculature and biopsy specimens show a high density of blood vessels in degenerated tendons [107,108]. This could result from expression of angiogenic factors. Vascular en-dothelial growth factor is highly expressed by degenerated Achilles tendons, whereas it is down-regulated in normal tendons . MRI appearance of Achilles tendon degeneration demonstrates tendon thickening (Fig. 48), retro-calcaneal fluid, peritendinous fluid/edema, and tendon tears , although there is some overlap in the imaging appearance between symptomatic and asymptomatic tendons . Tendon tear is seen as partial or complete discontinuity of tendon fibers (Fig. 49), or areas of fissuring or fluid signal intensity within the tendon. Treatment for tendinosis is conservative in most cases . In cases refractory to conservative management, surgical debridement of the diseased tendon is performed . In the setting of Achilles tendon tear, surgical repair is performed, sometimes with tendon augmentation from the FHL or peroneus brevis [111,112].
Haglund's syndrome is a painful condition of the heel, which occurs from mechanically induced inflammation of the retrocalcaneal bursa and the superficial tendo-Achilles bursa (Fig. 50) . Conflicting results have been reported for surgical treatment, which generally includes partial resection of the heel, with or without bursa resection [114,115]. Clinical outcome appears to depend partly on the amount of bone resected [113,114].
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