Mechanical response of ankle ligaments at low loads

METHODS: Eight fresh-frozen ankles (mean age 65) were dissected to expose the ligaments surrounding the talocrural joint. Eight ankle ligaments were studied and included: medially-anterior tibiotalar (ATTL), posterior tibiotalar (PTTL), tibiocalcaneal (TCL); laterally-anterior tibiofibular (ATiFL), posterior tibiofibular (PTiFL), anterior talofibular (ATFL), posterior talofibular (PTFL), and calcaneofibular (CFL). Stress relaxation tests were carried out at 30% and 10% strain. The peak load and area under the curve were assessed for all experiments.

RESULTS: Significant differences were found for the average peak loads of the elastic response between 30% and 10% strain for each ligament (p < .05). At 10% strain the relationship between the ligaments on the medial and lateral side revealed a Pearson R value of .991 (p = .087). No significant difference was found between the strain energies of the various ligaments (p > .05). The anterior talofibular ligament was found to possess similar relaxation results to the medial ligaments. The calcaneofibular ligament relaxed up to 10% more compared to the anterior talofibular for the same relaxation period. The mechanical testing was performed in uniaxial tension and did not consider off-axis loading that may occur in vivo during ankle motion.

CONCLUSIONS: The stress relaxation experiments revealed all ligaments to relax even when loaded to less than 5 N, reflecting the viscoelastic nature of ligaments.