How to diagnose plantaris tendon involvement in midportion Achilles tendinopathy - clinical and imaging findings

Background: The purpose of this investigation was to evaluate if clinical assessment, Ultrasound + Colour Doppler (US + CD) and Ultrasound Tissue Characterisation (UTC) can be useful in detecting plantaris tendon involvement in patients with midportion Achilles tendinopathy. Methods: Twenty-three tendons in 18 patients (14 men, mean age: 37 years and 4 women: 44 years) (5 patients with bilateral tendons) with midportion Achilles tendinopathy were surgically treated with a scraping procedure and plantaris tendon removal. For all tendons, clinical assessment, Ultrasound + Colour Doppler (US + CD) examination and Ultrasound Tissue Characterisation (UTC) were performed. Results: At surgery, all 23 cases had a plantaris tendon located close to the medial side of the Achilles tendon. There was vascularised fat tissue in the interface between the Achilles and plantaris tendons. Clinical assessment revealed localised medial activity-related pain in 20/23 tendons and focal medial tendon tenderness in 20/23 tendons. For US + CD, 20/23 tendons had a tendon-like structure interpreted to be the plantaris tendon and localised high blood flow in close relation to the medial side of the Achilles. For UTC, 19/23 tendons had disorganised (type 3 and 4) echopixels located only in the medial part of the Achilles tendon indicating possible plantaris tendon involvement. Conclusions: US + CD directly, and clinical assessment indirectly, can detect a close by located plantaris tendon in a high proportion of patients with midportion Achilles tendinopathy. UTC could complement US + CD and clinical assessment by demonstrating disorganised focal medial Achilles tendon structure indicative of possible plantaris involvement.