Anatomical and biomechanical study of the inferior extensor retinaculum by shear-wave elastography in healthy adults.

PURPOSE: The purpose of this study was to evaluate the stiffness of the inferior extensor retinaculum (IER) using shear-wave elastography (SWE) in neutral and varus positions in healthy adults, and to assess the reliability and reproducibility of these measurements. METHODS: Both ankles were analyzed by shear-wave elastography (SWE) in 20 healthy patients (10 females/10 males) resting on a hinge support with their ankles in neutral, valgus 20°, and varus 30° positions. Their stiffness was evaluated by shear-wave speed measured (SWS). RESULTS: The median SWS of the IER varies according to the position of the ankle. The IER tension was maximal in the 20° valgus position (4.1 m/s (52.8 kPa), ranged from 3.0 to 6.4 m/s), in contrast to the other positions (p < 0.0001). Retinaculum SWS was negatively correlated with age significantly in neutral (ρ = - 0.38, p = 0.02) and varus (ρ = - 0.47, p = 0.002) positions. Gender, dominant side, height, and foot morphology (foot arch, hind foot frontal deviation) had no impact on IER stiffness. Intra- and inter-observer agreements were all excellent. CONCLUSION: SWE is a reliable and reproducible technique for quantitative analysis of the stiffness of the main part of the IER: the frondiform ligament. It becomes taut in the valgus position of the ankle, and its strength decreases with age, even in young subjects. This could be an interesting diagnostic examination in cases of prolonged pain, and could help in the choice of transplant during surgical repair of the ATFL. LEVEL OF EVIDENCE: IV.