Biomechanics and Motion Analysis

Ankle Stability - Ligamentous and Articular Restraints

Principal Investigator: Harold B. Kitaoka, M.D.
Project Coordinator: Lawrence Berglund — berglund.lawrence@mayo.edu

Ligamentous structures around the ankle play an important role in stablizing the ankle. However the ligamentous contribution diminishes when the ankle is loaded. When loaded, the articular geometry of the ankle plays a dominant role in stablizing the ankle.

Tests were performed for three flexion angles (plantar flexion of 15 degrees, neutral and 10 degrees of dorsiflexion) Axial loads of 5 N or 700N were applied. Normal ankle stability and ankles with either the deltoid lateral and/or collateral ligaments sectioned. Load displacement curves were analyzed for laxity and stiffness.

There were some effects of ankle position on displacement in three directions. For medial translation, displacement was significantly larger in plantarflexion than in dorsiflexion for 5N axial load, and for 700N axial load displacement was significantly larger in plantarflexion than in neutral and dorsiflexion. For lateral translation, displacement was significantly larger in plantarflexion than in neutral and dorsiflexion in both 5N and 700N axial load conditions. For internal rotation, displacement was significantly larger in plantarflexion than in dorsiflexion for both 5N and 700N axial load conditions.

When little or no axial load is applied to the ankle, ligamentous structures play a dominant role in stabilization. The lateral collateral ligament was the primary restraint to anterior translation, and the deltoid to posterior displacement. Both are important for rotatory stability. Joint geometry is the primary stabilizer for M-L translation. Joint geometry is the primary factor once the ankle is loaded for all translatory motions, and a 60% contributor for rotatory stability when 700 N of axial load was applied.