[Biomechanics of the ligaments of the unstable ankle joint]

Ligament rupture occurs at the maximum breaking load. During ligament healing, contraction and remodeling of the scar is sufficiently advanced at 6 weeks to reach 60 to 70% of the initial strength. There is evidence of an early improvement in biomechanical properties of repaired ligaments. This advantage, however, may not be sustained as, after one year, sutured and unsutured ligaments have nearly equal length when measured at rest and comparable failure strength when subjected to exercise. Each of the ankle ligaments has a role in stabilizing the ankle and/or subtalar joint. Beside of maintaining lateral ankle stability, the lateral ankle ligaments have been shown to play a significant role in providing rotational ankle stability. This is especially true for the anterior talofibular ligament. A loss of this ligament does allow for an increase in foot inversion and external rotation of the leg to occur, without any tilting of the talus or subtalar gapping. It is this increase in foot inversion which may lead to a symptomatic instability. When treating ankle instability, it is therefore important for the clinician to take the alteration of hindfoot biomechanics into consideration. This is especially the case for any surgical repair of injured ankle ligaments. Unphysiological tenodesis procedures should be avoided.