Biomechanical Assessment of Syndesmotic and Deltoid Ligament Strain in Pronation-External Rotation Type Ankle...

Area of Science:

• Biomechanics
• Orthopedic Surgery
• Computational Modeling

Background:

• Suprasyndesmotic ankle fractures often result from pronation-external rotation (PER) mechanisms.
• Traditional views associate PER injuries with complete syndesmotic ligament disruption or medial malleolus fracture.
• Emerging evidence suggests certain key stabilizing ligaments may remain intact, impacting talocrural stability.

Purpose of the Study:

• To evaluate modelled ligament tension patterns in pronation-external rotation (PER) ankle injuries.
• To utilize a validated musculoskeletal computer simulation model for assessing ligament strain.
• To investigate the sequence and magnitude of ligament loading during simulated PER injuries.

Main Methods:

• A musculoskeletal ankle joint model was developed using the AnyBody Modeling System.
• The pronation-external rotation (PER) mechanism was simulated via external rotation (0-50 degrees) with a fixed foot.
• Ligament tensional forces for the deltoid and syndesmotic complexes were recorded; fibular fracture was excluded due to model limitations.

Main Results:

• Anterior and superficial deltoid ligaments and the anterior inferior tibiofibular ligament (AITFL) showed significant tension increases.
• The deep posterior tibiotalar ligament (dPTTL) and posterior inferior tibiofibular ligament (PITFL) exhibited minimal strain.
• These findings suggest the dPTTL and PITFL may remain intact in a subset of PER injuries.

Conclusions:

• Computer simulation of PER injuries indicates lower tensional forces on the posterior ligaments.
• This challenges traditional injury cascade models, such as the Lauge-Hansen classification.
• Computer modeling offers a viable alternative to in vitro biomechanical studies for hypothesis generation and injury classification.