Fixed and mobile-bearing total ankle prostheses: Effect on tibial bone strain

Area of Science:

• Orthopedic biomechanics
• Biomaterials engineering
• Finite element analysis

Background:

• Total ankle replacement (TAR) has a high revision rate, necessitating improved implant survival.
• The biomechanical advantages of fixed-bearing versus mobile-bearing prostheses in TAR remain unclear.

Purpose of the Study:

• To compare biomechanical factors associated with implant failure in fixed-bearing and mobile-bearing total ankle prostheses.
• To test the hypothesis that different bearing types influence bone strain, interfacial stress, and bone support.

Main Methods:

• A validated finite element model simulated three conditions: fixed-bearing, centered mobile-bearing, and eccentric mobile-bearing prostheses.
• Simulations used maximum axial compression force on seven tibias during walking.
• Evaluated bone strain, bone-implant interfacial stress, and bone support, and their correlations.

Main Results:

• No statistically significant biomechanical differences were found between the three prosthesis configurations.
• Bone support was primarily trabecular and less effective posteriorly.
• Bone strain and bone-implant interfacial stress strongly correlated with bone support.

Conclusions:

• Slight biomechanical differences between fixed and mobile bearing prostheses were insufficient to declare superiority under axial compression.
• The study provides no evidence to caution surgeons against using two-component fixed-bearing implants, considering published clinical outcomes.