Calcaneofibular ligament may act as a tensioner of peroneal tendons as revealed by a contactless three-dimensional scan system on cadavers.

The ligaments are believed to have a role in stabilizing joints and regulating joint motion. Here, we propose a novel function of the calcaneofibular ligament (CFL), which stabilizes the ankle joint. In human bipedal locomotion, the peroneal muscles maintain mediolateral stability and prevent involuntary ankle inversion. To investigate the functional relationship between the peroneal longus tendon (PLT), brevis tendon (PBT), and CFL, we quantitatively analyzed the positional changes of the tendons by using a contactless three-dimensional optical scan system. Eighteen cadaveric specimens were included in the study. Interestingly, with increased tension of the CFL, the tendons significantly moved toward the lateral direction (P < 0.001), compared with their position when the CFL was detached. The actual lift amount reached 2.0 ± 0.8 mm for the PLT and 1.9 ± 1.0 mm for the PBT. These results strongly suggest that a tensed CFL can lift the peroneal tendons and may act as a "tensioner" for the effective transmission of muscle contraction. This phenomenon contributes to postural control, especially in regaining balance on uneven terrain, and provides a new perspective for the exercise methods or understanding the ankle joint instability due to sprains.