Achilles tendon tear

Last revised by Henry Knipe on 31 Jan 2024

Achilles tendon tears are the most common ankle tendon injuries, with microtears to full thickness tendon tears of the Achilles tendon and are most commonly seen secondary to sports-related injury, especially squash and basketball.

There is strong male over-representation presumably as a result of the predominantly sport-related etiology. Patients are typically aged 30-50 years and have no antecedent history of calf or heel pain. There are however numerous recognized predisposing factors including:

Typically patients present with sudden onset of pain and swelling in the Achilles region, often accompanied by an audible snap during forceful dorsiflexion of the foot. A classic example is that of a 'weekend warrior' playing squash.  

If complete a defect may be felt and the patient will have only minimal plantar flexion against resistance. Clinical examination can be used in aiding diagnosis:

  • calf-squeeze (Thompson) test

    • examines the integrity of the Achilles tendon by squeezing the calf

    • positive when foot does not move or minimally plantarflexes 10

    • sensitivity 96%, specificity 93%, positive likelihood ratio 13.71, negative likelihood ratio 0.04 (NB based on one study) 10

The spectrum of tears ranges from microtears to interstitial tears (parallel to the long axis of the Achilles), to partial tears, and eventually to complete tears (ruptures).

Tears can be acute or chronic, with repeated minor trauma. At the mildest end of the spectrum all that may be present is peritendonitis.

Typically, in a young individual with a normal Achilles tendon ruptures in the 'critical zone', which is a region of relative watershed hypovascularity 2-6 cm proximal to insertion. 

Plain radiographs may show soft tissue swelling and obliteration of pre-Achilles fat pad (Kager's triangle).

For partial thickness tears, there is often enlargement of the tendon ( >1 cm) with abnormally hypoechoic or anechoic areas within which correspond to the tear and associated adjacent tendinosis.

For full thickness tears, ultrasound often shows separation of the torn ends with a contour change of the tendon. Also, acoustic shadowing at the margins of the tear from sound beam refraction, and adjacent hypoechoic tendinosis.

Appearances can vary:

  • a full-thickness tear often shows a tendinous gap filled with edema or blood

  • complete rupture shows retraction of tendon ends

When a plantaris muscle is present then its tendon is usually spared due to its more anterior insertion on the calcaneum.

  • T2: partial thickness or interstitial tears may show high signal on long TR, and tendon swelling to >7 mm AP

  • post-operative MR imaging may show a tendon gap although this tends to resolve in around 12 weeks 8

  • post-operatively, Achilles tendon may appear thicker on MR follow up 9

Treatment depends on the extent of the tear. Partial thickness tears can initially be treated conservatively, with surgery reserved for failure of conservative management, or in some cases for high-performance athletes. Full-thickness tears are normally surgically repaired. If the patient is not deemed suitable for surgical repair (frail, ill, etc.) casting of the ankle in the talipes equinus position may be an alternative.

Surgical repair results in a shorter Achilles tendon and better greater calf muscle strength (less soleus atrophy) than non-surgical treatment 10.

A true rupture of the Achilles tendon was first described by Ambroise Pare in 1575 and first reported in the medical literature in 1633 3.

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