Objective: The purpose of this study is to assess the elastic and anisotropic properties of normal calcaneal tendon in vivo by transient shear wave elastography (SWE).
Materials and methods: This study was approved by our institutional ethics committee. Eighty healthy subjects over 18 years of age were prospectively included. Data on the patients' height, weight, sporting activities, and take-off foot were assessed. The thickness, width, and cross-sectional area of the calcaneal tendons were measured. The shear wave propagation velocity (Vmean) was measured by three radiologists on axial and sagittal SWE images at four different degrees of ankle flexion, enabling to calculate elasticity modulus (Emean), and relative anisotropy coefficient (A) values.
Results: In complete plantar flexion, Vmean was 6.8 ± 1.4 m.s(-1) and 5.1 ± 0.8 m.s(-1), respectively, on the sagittal and axial SWE image, resulting in an elastographic anisotropy A of 0.24 ± 0.16. The best interobserver correlation coefficient of Emean and Vmean was 0.43 and 0.46, respectively, in the sagittal SWE for complete plantar flexion. Vmean and Emean significantly increase when the tendon is stretched by ankle dorsiflexion. The maximal values in sagittal SWE were Vmean = 16.1 ± 0.7 m.s(-1), Emean = 779.5 ± 57.1kPa and A = 0.63 ± 0.07.
Conclusions: SWE allows the elastic properties of the calcaneal tendon to be evaluated quantitatively in vivo, but interobserver reproducibility is questionable. It confirms the tendinous elastographic anisotropy and stiffness augmentation of stretched tendon.