Plantaris friction syndrome

Case contributed by Amit Lakkaraju
Diagnosis almost certain


Postero-medial left ankle pain and stiffness. Clinically has a tender lump postero-medial Achilles tendon and crepitus.

Patient Data

Age: 70 years
Gender: Male

Achilles tendinosis and paratenon edema. Mucoid degeneration is seen on the medial Achilles tendon. The plantaris tendon is seen on the medial side of the Achilles tendon. At the site of impingement, the plantaris tendon "disappears". This is due to the degree of edema and attrition of the plantaris tendon. Mucoid degeneration is seen in the Achilles tendon at the site of impingement.


Ultrasound of the left Achilles tendon in the same patient shows fusiform enlargement of the Achilles tendon. Plantaris tendon is annotated running medial to the Achilles tendon. There is hypervascularity of the Achilles tendon. The power Doppler images show this is predominantly medial sided hypervascularity occurring at the site of plantaris friction.

Case Discussion

Plantaris friction syndrome is a relatively rare cause of Achilles tendinosis. It presents with localized medial sided pain in the mid Achilles tendon. Clinically there is a tender lump, crepitus and reproduction of pain on repeated ankle plantar and dorsiflexion.

Ultrasound shows the plantaris tendon is either thickened or thin secondary to attrition. There is a fusiform mid-Achilles tendinosis, largest diameter at the site of plantaris friction. Mucoid degeneration is also seen focally on the medial aspect of the tendon at the site of friction. There is inflammatory change on B-mode images and hypervascularity on color Doppler images. This site is focally tender on palpation with the probe.

On MRI. there are very similar changes. There is a fusiform mid-Achilles tendinosis. Mucoid degeneration/localized tendon high signal occurs on the medial side of the Achilles tendon at the site of plantaris impingement. There is asymmetric paratenon thickening or paratenon edema.

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