In vivo ultrasonographic evidence that tensed calcaneofibular ligament consistently lifts the peroneal tendons.

A recent cadaveric study demonstrated that when the calcaneofibular ligament (CFL) is tensed, it lifts the peroneal tendons, suggesting that the CFL acts as a mechanical tensioner to facilitate efficient transmission of peroneal muscle contractions. We investigated this phenomenon in vivo using a quantitative assessment with an ultrasound system equipped with strain elastography. Twenty-six ankles from 13 healthy participants were prospectively examined. A 20° inversion, intended to tense the CFL, was induced by tilting the lower leg and was compared to the neutral position. The distance between the peroneal tendons and a defined calcaneal reference point was significantly greater at 20° inversion than at neutral (P < 0.001), along with a significant increase in relative CFL stiffness as determined by strain elastography (P < 0.001) and varying degrees of deformation in the cross-sectional morphology of the peroneal tendons. These results strongly suggest that peroneal tendons are lifted by a tensed CFL in vivo. Notably, lifting was consistently observed in all the participants, indicating a reproducible and likely universal mechanism. This purely mechanical interaction may enhance muscular force transmission through tendon preloading, particularly under weight-bearing conditions, and increase the lever arm at the talocrural and subtalar joints, thereby improving the torque generation during movement.