Ultrasonographic measurements of gastro-soleus fascia thickness in midportion Achilles tendinopathy: A case-control study

Background: The Achilles tendon is one of the thickest, largest, and strongest tendons in the human body. Biomechanically, the AT represents the conjoint tendon of the triceps surae muscle, placed in series with the plantar fascia (PF) to ensure force transmission from the triceps surae toward the toes during walking, running, and jumping. Commonly encountered in the diagnostic evaluation of heel pain, Achilles tendinopathy (AT) refers to a combination of pathological changes affecting the tendon itself often resulting from excessive repetitive stress and overuse. Nevertheless, increasing evidence demonstrates that structural alterations due to overuse or abnormal patterns of skeletal muscle activity are not necessarily restricted to the muscles or tendons but can also affect the fascial tissue. At the same time, there has been recent discussion regarding the role of the fascial tissue as a potential contributor to the pathophysiological mechanisms of the development of several musculoskeletal disorders including tendinopathies. To the best of our knowledge, ultrasound (US) imaging studies on the fascial structures related to the triceps surae complex, as well as their possible correlation with Achillodynia have never been presented in the current literature. Methods: In the present study, a comparative US imaging evaluation of textural features of the suro-Achilleo-plantar complex was performed in 14 healthy controls and 14 symptomatic subjects complaining of midportion AT. The thickness of the Achilles tendon, paratenon, intermuscular fascia, and PF has been assessed with US. In addition, both groups underwent the Victorian Institute of Sport Assessment-Achilles (VISA-A), a disease-specific questionnaire that measures the severity of symptoms of AT. Correlations between quantitative ultrasound measures and VISA-A scores were determined through Pearson or Spearman's rho correlations. Results: Our ultrasonographic findings revealed statistically significant differences (p<0.05) in Achilles tendon and paratenon thicknesses between AT patients and controls. No significant differences were observed between groups in PF at the calcaneal insertion as all mean measures were within the expected range of a normal PF on US imaging. In contrast, in tendinopathic subjects, the deep intermuscular fascia between medial gastrocnemius (MG) and soleus (SOL) muscles is significantly (p<0.01) and considerably thickened compared to those of healthy subjects. Moderate correlations exist between tendon and paratenon thicknesses (r= 0.54, p= 0.04) and between MG-SOL fascia and tendon thicknesses (r= 0.58, p= 0.03). Regarding symptom severity and US morphological findings, the Spearman rho test showed no correlation. Conclusions: Our data demonstrate that, in symptomatic subjects, US alterations are not restricted to paratenon and intratendinous areas, but also affect upstream structures along the myofascial chain, resulting in thickening of the fascia interposed between MG and SOL muscles. Moreover, positive correlations were found between MG-SOL fascia thickening and abnormalities in AT, paratenon, and symptom severity. Thus, US alterations in the fascial system should be interpreted within the clinical context of patients with AT as they may in turn represent important predictors of subsequent clinical outcomes and could help healthcare professionals and clinicians to refine non-operative treatment strategies and rehabilitation protocols for this disease.