Both the plantaris tendon and the peroneus tertius tendon are used as auto- and allogenous graft materials to reconstruct the ankle ligament complex. However, it is unclear to what extent these graft materials resemble the load-deformation behavior of the ankle ligaments. A total of 34 human ankle ligaments and 35 tendons were assessed mechanically deploying a quasi-static tensile testing setup. Tendons were significantly stiffer (median elastic moduli: plantaris tendon = 465.7 MPa, peroneus tertius tendon = 338.5 MPa, medial ligament = 61.4 MPa, lateral ligament = 49.3 MPa; p ≤ 0.035), but more distensible (median strain at maximum force: plantaris tendon = 15.1%, peroneus tertius tendon = 15.3%, medial ligament = 9.3%, lateral ligament = 9.6%; p ≤ 0.008) and mechanically tougher (median ultimate tensile strength: plantaris tendon = 51.0 MPa, peroneus tertius tendon = 40.5 MPa, medial ligament = 4.1 MPa, lateral ligament = 3.5 MPa; p ≤ 0.033) when compared to medial and lateral ankle ligaments. The lateral ligaments of the right ankle were significantly tougher compared to the left side (p = 0.015). The elastic modulus of the medial ligament (r = 0.489, p = 0.045) and the peroneus tertius tendon (r = 0.517, p = 0.014) yielded an age-dependent increase. Both tendons seem biomechanically suitable graft materials to replace the medial and lateral ankle ligaments during physiological loading. The age-dependent increase in tissue elastic properties of the medial vs. lateral ankle ligaments, and differences in ultimate tensile strength between the lateral ligaments left vs. right, may reflect the complex asymmetric loading behavior of both ankle ligaments.
