A framework for parametric modeling of ankle ligaments to determine the in situ response under gross foot motion

Abstract

Ligament sprains account for a majority of injuries to the foot and ankle complex, but ligament properties have not been understood well due to the difficulties in replicating the complex geometry, in situ stress state, and non-uniformity of the strain. For a full investigation of the injury mechanism, it is essential to build up a foot and ankle model validated at the level of bony kinematics and ligament properties. This study developed a framework to parameterize the ligament response for determining the in situ stress state and heterogeneous force–elongation characteristics using a finite element ankle model. Nine major ankle ligaments and the interosseous membrane were modeled as discrete elements corresponding functionally to the ligamentous microstructure of collagen fibers and having parameterized toe region and stiffness at the fiber level. The range of the design variables in the ligament model was determined from existing experimental data. Sensitivity of the bony kinematics to each variable was investigated by design of experiment. The results highlighted the critical role of the length of the toe region of the ligamentous fibers on the bony kinematics with the cumulative influence of more than 95%, while the fiber stiffness was statistically insignificant with an influence of less than 1% under the given variable range and loading conditions. With the flexibility of variable adjustment and high computational efficiency, the presented ankle model was generic in nature so as to maximize its applicability to capture the individual ligament behaviors in future studies.

Keywords:

• Parametric modeling
• finite element ankle model
• collagen fibers
• design of experiment
• sensitivity study
• computational biomechanics

Acknowledgements

One of the co-authors (Kent) has an ownership interest in one of the sponsors of the study (Biocore). The authors would like to thank the members of the Foot & Ankle Subcommittee of the National Football League for funding, supporting and providing valuable input to this study. Additionally, the authors would like to thank Dr. Yue Zhang from BMO Harris Bank for providing valuable discussion and comments regarding the DOE sampling theme. The authors are also immensely grateful to Tim Gillispie for his thorough review and insightful comments.

Disclosure statement

No potential conflict of interest was reported by the authors.