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Apr 21st

MRI and Ultrasound of the Achilles Tendon

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The Achilles tendon, also known as the tendo Achilles, tendo calcaneus or calcaneal tendon, is the longest tendon of the body, formed by the union of the lower aspect of the calf muscles (gastrocnemius, soleus and the variably present plantaris muscle).

The tendon inserts by way of a broad insertion on the calcaneus (heel bone) of the hindfoot. During development, the Achilles tendon is continuous with the broad flat tendon of the foot known as the plantar fascia (figure 1).

Normal MRI of the Achilles tendon (figure 1) and ultrasound of normal Achilles tendon

Figure 1. Normal MRI of the Achilles tendon demonstrates this to be a well defined hypointense (dark) structure (arrow) inserting onto the calcaneus, thereafter becoming continuous with the plantar fascia (arrow).

Figure 2: Ultrasound of a normal Achilles tendon depicts the multiple small fibrils that make up the tendon as alternating bright and dark lines (arrow). Note the calcaneal insertion.

As for any tendon, degeneration due to wear and tear may occur, known as tendinosis (incorrectly frequently referred to as tendinitis). Achilles tendinosis results in pain during activities such as running and may be seen in combination with degeneration of the plantar fascia (plantar fasciitis, or “heel spurs”) and strains of the calf muscles [1].

Most cases of tendinosis resolve with conservative therapy, which consists of exercises, eccentric strengthening, heel inserts and activity modification.

If severe, the tendinosis may not respond to such treatment, hence requiring injection therapy, using autologous blood, platelet rich plasma, autologous tenoctyes or polidocanol (figure 3).

Ultrasound guided polidocanol injection into the mid Achilles tendon

Figure 3: Ultrasound guided polidocanol injection into the mid Achilles tendon.

Initially, imaging with either an ultrasound (figure 2) or an MRI is performed in order to determine the degree and extent of the tendinosis, as well as the presence of any tears and surrounding inflammation (paratenonitis, retrocalcaneal and/or retroAchilles bursitis).

Achilles tendinosis typically involves the mid portion of the tendon (figure 4) and left untreated, may result in dramatic painful rupture (figure 5) with sudden loss of function, warranting surgery.

MRI of severe Achilles tendinosis

Figure 4: MRI of severe Achilles tendinosis is characterised by marked thickening, increased signal intensity (brightness) and areas of intrasubstance tearing of the tendon, placing the tendon at risk of full thickness rupture.

MRI of a patient, demonstrates a full thickness tear of the Achilles tendon

Figure 5: MRI of a patient suffering from severe pain following a jumping injury demonstrates a full thickness tear of the Achilles tendon, with recoiling of the tendon edges and haemorrhage in the surrounding soft tissues.

Less frequently, the tendinosis may involve the insertion of the Achilles onto the calcaneus (known as enthesopathy) and may be seen in conjunction with certain arthritic diseases, as well as increasing age (figure 6). In this instance, changes within the bone may be seen, such as fluid (oedema) and prominence of the calcaneus, known as Haglund’s deformity.

MRI of Achilles insertional tendinosis (enthesopathy)

Figure 6: MRI of Achilles insertional tendinosis (enthesopathy) is characterised by bone marrow oedema (arrow) of the calcaneus (heel bone), Haglund’s deformity, inflammation in the surrounding soft tissues (retrocalcaneal bursitis; arrow) and partial thickness insertional tendon tearing (arrow).

References

  1. Koulouris G, Ting AY, Jhamb A, Connell D, Kavanagh EC. Magnetic resonance imaging findings of injuries to the calf muscle complex. Skeletal Radiol (10):921-7, 2007
  2. Pavlov H, Heneghan MA, Hersh A, Goldman AB, Vigorita V. The Haglund syndrome: initial and differential diagnosis. Radiology. 1982 Jul;144(1):83-8.

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