Achilles Tendon Rupture

Ruptures of the Achilles tendon most commonly occur spontaneously in healthy, young, active individuals who are aged 30-50 years and have no antecedent history of calf or heel pain. Unlike tears or ruptures at the musculotendinous junction of the Achilles tendon (tennis leg), Achilles tendon ruptures are located within the tendon substance itself, approximately 1-2 inches proximal to its insertion into the calcaneus. Poor conditioning, advanced age, and overexertion are risk factors for this injury. However, the common precipitating event is a sudden eccentric force applied to a dorsiflexed foot. Ruptures of the Achilles tendon also may occur as the result of direct trauma or as the end result following Achilles peritenonitis with or without tendinosis.
Achilles tendon pathology, other than rupture, can be classified into a spectrum of injuries including peritenonitis, tendinosis, and peritenonitis with tendinosis. Patients with peritenonitis experience localized burning pain along the tendon during or following activities; as the disease progresses, onset of pain may occur earlier during activities, with decreased activity level, or even at rest. Tendinosis usually is comprised of an asymptomatic, noninflammatory, degenerative disease process (mucoid degeneration); patients with tendinosis may complain of a sensation of fullness or a nodule in the back of the leg. Peritenonitis with tendinosis is comprised of activity-related pain, diffuse swelling of the tendon sheath, and presence of nodules. Treatment of these entities is not discussed in this article.
Frequency
United States
The true prevalence of Achilles tendon rupture is unknown, although it occurs more commonly in men who are in their third to fifth decade of life and who participate in recreational activities.

Functional Anatomy
The Achilles tendon, coined after the mythologic Greek god, is the largest and strongest tendon in the human body. The Achilles tendon is formed from the tendinous contributions of the gastrocnemius and soleus muscles coalescing approximately 15 cm proximal to its insertion. Along its course in the posterior aspect of the leg, the tendon spirals 30-150° until it inserts into the calcaneal tuberosity. The gliding ability of the Achilles tendon is aided by a thin sheath of paratenon rather than a true synovial sheath. The sheath of paratenon is composed of a visceral layer and a parietal layer.
The blood supply of the Achilles tendon arises from its osseous insertion, its musculotendinous junction, and multiple infiltrating mesosternal vessels, which cross the layers of the anterior paratenon. Various injection and nuclear medicine studies have demonstrated a paucity of mesosternal and intratendinous vessels 2-6 cm proximal to the heel insertion (ie, the watershed area). Due to the relative lack of blood supply in this area, the tendon is less resilient to repetitive microtrauma and has a higher tendency for irritation, degeneration, and rupture.
Sport Specific Biomechanics
The entire gastrocnemius-soleus musculotendinous unit spans the knee, tibiotalar (ankle), and talocalcaneal (subtalar) joints. Contracture of this complex flexes the knee, plantar flexes the ankle, and supinates the subtalar joint. The function of the gastrocnemius-soleus musculotendinous unit is necessary in running, jumping, toe standing, and stair-climbing activities because it forcefully plantar flexes the ankle. During running, forces 10 times the body weight have been measured within the tendon substance.

Read more HERE