The in situ force in the calcaneofibular ligament and the contribution of this ligament to ankle joint stability.

BACKGROUND Numerous biomechanical studies of the lateral ankle ligaments have been reported; however, the isolated function of the calcaneofibular ligament has not been clarified. We hypothesize that the calcaneofibular ligament would stabilize the ankle joint complex under multidirectional loading, and that the in situ force in the calcaneofibular ligament would change in each flexed position. METHODS Using seven fresh frozen cadaveric lower extremities, the motions and forces of the intact ankle under multidirectional loading were recorded using a 6-degree-of-freedom robotic system. On repeating these intact ankle joint complex motions after the calcaneofibular ligament transection, the in situ force in the calcaneofibular ligament and the contribution of the calcaneofibular ligament to ankle joint complex stability were calculated. Finally, the motions of the calcaneofibular ligament-transected ankle joint complex were recorded. FINDINGS Under an inversion load, significant increases of inversion angle were observed in all the flexed positions following calcaneofibular ligament transection, and the calcaneofibular ligament accounted for 50%-70% of ankle joint complex stability during inversion. The in situ forces in the calcaneofibular ligament under an anterior force, inversion moment, and external rotation moment were larger in the dorsiflexed position than in the plantarflexed position. INTERPRETATION The calcaneofibular ligament plays a role in stabilizing the ankle joint complex to multidirectional loads and the role differs with load directions. The in situ force of the calcaneofibular ligament is larger at the dorsiflexed position. This ligament provides the primary restraint to the inversion ankle stability.