Discordance in Achilles Tendon Assessment between Radiography and Ultrasonography due to Torsion

Tendon xanthomas are part of the clinical triad of diagnostic criteria for familial hypercholesterolemia (FH) in Japan. The Achilles tendon generally has a twisted structure, and we investigated the impact of torsion on Achilles tendon thickness (ATT) assessment.

In this single-center retrospective study, 61 acute coronary syndrome (ACS) patients who underwent ATT assessment using radiography (ATT-Xp) and ultrasonography (ATT-US) were analyzed. Ultrasonographic ATT assessment used two axes - antero-posterior axis (ATT-US (AP)) and corrected axis according to Achilles tendon torsion (ATT-US (correct)) - and the torsion angle was measured. The association of torsion with each ATT assessment was investigated.

The torsion angle of the Achilles tendon varied widely. Both ATT-US (AP) and ATT-US (correct) were significantly correlated with ATT-Xp, although the correlation between ATT-Xp and ATT-US (correct) was modest compared to the correlation with ATT-US (AP) (ATT-US (AP)-Right: r= 0.91, p＜0.001, Left: r= 0.91, p＜0.001; ATT-US (correct)-Right: r = 0.82, p＜0.001, Left: r = 0.76, p＜0.001, respectively). Torsion angle was well correlated with the differences in ATT between ATT-Xp and ATT-US (correct) (Right: r= 0.62, p＜0.001, Left: r= 0.66, p＜0.001). There were no independent factors associated with Achilles tendon torsion.

This is the first study to quantitatively evaluate the three-dimensional twisted structure of the Achilles tendon and demonstrate that Achilles tendon torsion is associated with the difference between ATT-Xp and ATT-US (correct). Torsion of the Achilles tendon should be considered in Achilles tendon assessment, particularly radiographical assessment.