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Disorders of the Insertion of the Achilles Tendon and Achilles Tendinitis*t
Because of its size and unique functional anatomy, the Achilles tendon is susceptible to both acute and chronic injury. This paper addresses some of these injuries, including the various forms of tendinitis as well as the various pain syndromes of the retrocalcaneal space, such as retrocalcaneal bursitis and Haglund deformity. Functional and Gross Anatomy The Achilles tendon is the continuation of the triceps surae, which originates from the medial and lateral femoral condyles as the two heads of the gastrocnemius and continues as the gastrocnemius blends with the soleus distally. The Achilles tendon inserts onto the middle third of the posterior tuberosity of the calcaneus. At the bone-tendon junction, the enthesis is composed of calcified and noncalcified cartilage. Paratenon surrounds the tendon and is able to stretch two to three centimeters with movement of the tendon, thereby allowing the Achilles tendon to glide smoothly. The tendon is vascularized by anterior muscular branches as well as osseous and periosteal vessels near the site of insertion. Although there is both a proximal and a distal intratendinous vascular supply, there are considerably fewer vessels four centimeters proximal to the calcaneus than anywhere else in the tendon57". Thus, the region of the tendon three to five centimeters proximal to the insertion is a relatively avascular zone and is the area most prone to various pathological problems, including chronic tendinitis and rupture. It is assumed that this hypovascularity is one of the causes of rupture.
The anatomical structures that make up the posterior aspect of the heel are the Achilles tendon, the posterior aspect of the calcaneus, the retrocalcaneal bursa, and the pretendinous bursa. The retrocalcaneal bursa lies anterior to the posterosuperior calcaneal tuberosity and lubricates the anterior aspect of the tendon as well as the superior aspect of the calcaneus'4. It is important to recognize that there is a normal communication between the posterior aspect of the Achilles tendon and the retrocalcaneal bursa, and retrocalcaneal injection of steroids may adversely affect the insertion of the tendon. If the posterosuperior and lateral process of the calcaneus is enlarged, it is referred to as a Haglund deformity"8. The enthesis, the bursa, and the bursal walls form a complex insertional...