Arc Test | Achilles tendinopathy / Achilles Tenosynovitis Assessment

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Arc Test | Achilles tendinopathy / Achilles Tenosynovitis Assessment

Diagnosing Achilles tendinopathy might seem straightforward, but there are countless differential diagnoses such as retrocalcaneal bursitis, bone anomalies such as a painful os trigonum, tarsal tunnel syndrome, and neuritis of the sural nerve amongst others. Furthermore, we will have to distinguish between an irritation of the tendon sheath often caused by friction overload and the tendon itself which are both managed differently.

In a meta-analysis by Reiman et al. (2014), the Arc test had a sensitivity of 42% and a specificity of 88% in the detection of midportion Achilles tendinopathy. We have to be careful though as the included studies used ultrasound as the gold standard and we have to keep in mind that many asymptomatic tendons will show pathology. For this reason, we give this test a rather weak value in clinical practice.

To conduct the test, have the patient lie on the examination table in prone position with the ankles clear of the table. First, the clinician palpates the Achilles tendon in a distal to proximal direction, between 2 and 6 cm above the insertion into the calcaneum gently squeezing the tendon between the index finger and the thumb feeling for localized thickening of the tendon. Afterward, the palpating fingers stay on the area of swelling and the patient is asked to dorsiflex and plantarflex the ankle.

In tendinopathy of the main body of the tendon, the area of swelling moves with dorsiflexion and plantarflexion. If an area of swelling cannot be identified, an area in the tendon 3cm proximal to the calcaneal insertion is palpated during the movement. If the palpable thickening does not move but stays relatively still with palpable crepitations, the tendon sheath might be suspected as the area of injury. The use of a stethoscope might be a helpful addition in case crepitations cannot be felt.