1The Bioengineering Laboratory, Department of Orthopaedic Surgery, Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street – GRJ 1215, Boston, MA 02114, USA
Background: Despite the numerous in-vitro studies on the mechanical properties and simulated injury mechanisms of the anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL), the in-vivo biomechanical behavior of these two ligaments has not yet been described.
Methods: Apparent length of the ATFL and CFL was measured in four ankles in healthy male subjects between 32 and 45 years of age (two left and two right) during a dorsiflexion-plantarflexion and supination-pronation arc of motion using a combined dual-orthogonal fluoroscopic and magnetic resonance imaging technique.
Results: The ATFL elongated from the neutral position at 16.3 +/- 3.0 mm to 20.8 +/- 2.7 mm at maximal plantarflexion and shortened significantly from the neutral position to 13.9 +/- 2.9 mm at maximal dorsiflexion (p = 0.01). The CFL shortened from the neutral position at 28.0 +/- 2.9 mm to 26.6 +/- 2.2 mm at maximal plantarflexion (p = 0.08) and elongated significantly from the neutral position to 29.9 +/- 3.0 mm at maximal dorsiflexion (p = 0.003). The ATFL elongated significantly from 14.8 +/- 2.5 mm at maximal pronation to 17.4 +/- 3.0 mm at maximal supination (p = 0.08). At the same time, the CFL shortened from 31.0 +/- 3.8 mm at maximal pronation to 26.9 +/- 3.6 mm at maximal supination (p = 0.02).
Conclusion: The results showed that the ATFL elongates more during plantarflexion and supination whereas the CFL increases in length with dorsiflexion and pronation. Concurrently, these data also demonstrated the reciprocal function between the two ligaments. While one shortens, the other one elongates. The different elongation of the ATFL and CFL during the same motion arc suggests that under excessive loading conditions the ATFL might be more vulnerable in plantarflexion and supination while the CFL might be more susceptible to injury in dorsiflexion and pronation. Furthermore, in the case of surgical reconstruction the grafts used to reconstruct the two ligaments may need to be tensioned at different positions of the ankle in order to reproduce their natural in vivo function.