Total ankle replacement design and positioning affect implant-bone micromotion and bone strains

Area of Science:

• Orthopedic biomechanics
• Biomaterials engineering
• Surgical outcomes research

Background:

• Implant loosening is a primary cause for total ankle replacement (TAR) revision, often associated with initial micromotion.
• Finite element modeling (FEM) has not been applied to assess TAR micromotion, and the biomechanical effects of malpositioning are unknown.

Purpose of the Study:

• To estimate implant-bone micromotion and peri-implant bone strains for optimally positioned and malpositioned TAR prostheses.
• To identify fixation features and malpositioning scenarios that increase the risk of loosening.

Main Methods:

• Developed FEMs for three common TAR devices (BOX, Mobility, Salto) implanted in the tibia/talus.
• Simulated physiological loads to assess micromotion and bone strains under various positioning scenarios.

Main Results:

• Mobility and Salto components showed the highest tibial and talar micromotion, respectively.
• Any malpositioning creating a bone-implant gap substantially increased micromotion and bone strains.
• Incomplete seating led to significantly elevated micromotion and bone strains.

Conclusions:

• Fixation closer to the joint line and/or using multiple pegs can improve primary stability.
• Incomplete seating of TAR implants is a critical factor increasing the risk of loosening and failure.