Mechanical characterisation of the lateral collateral ligament complex of the ankle at realistic sprain-like strain rates

BACKGROUND; Synthetic interventions continue to evolve with the progression made in materials science, surgical technologies and surgical methods. To facilitate the evolution of synthetic devices for lateral ankle repair a better understanding of the mechanical properties and failure mechanisms of the lateral collateral ligament (LCL) complex is required. This study aimed to improve understanding of the mechanical properties and failure modes of the LCL complex at strain rates representative of sprain.

METHOD; The LCLs were dissected from six human cadavers to produce individual bone-ligament-bone specimens. A mechanical testing device uni-axially loaded the ligaments in tension. Initially, preconditioning between 2 N and a load value corresponding to 3.5% strain was conducted for 15 cycles, before extension to failure at strain rate of 100%.s−1. The results were stratified by age, weight and body mass index (BMI) to explore potential correlations with ligament ultimate failure load or ligament stiffness.

RESULTS; The mean ultimate failure loads and the 95% confidence intervals for the ATFL, calcaneofibular (CFL) and posterior talofibular (PTFL) ligaments were 351.4 ± 110.8 N, 367.8 ± 79.8 N and 263.6 ± 164.3 N, respectively. A strong positive Pearson correlation was found between BMI and ultimate failure load of the CFL (r = 0.919; P = .01). A non-significant relationship was found between the mechanical properties and both age and weight. The ATFL avulsed from the fibula four times, the CFL avulsed from the fibula twice, the PTFL avulsed from the talus twice and all remaining failures were mid-substance.

CONCLUSION; The results identify the forces required to induce failure of the individual ligaments of the LCL complex and the related failure modes of individual ligaments. A correlation between BMI and the ultimate failure load of the CFL and PTFL may exist, although a greater sample size is required for confirmation.