Influence of taper design and loading on taper micromotion

Area of Science:

• Biomaterials engineering
• Orthopedic biomechanics
• Tribology

Background:

• Modular total hip replacements (THRs) are susceptible to failure due to debris generated at the bore-trunnion interface.
• Fretting and corrosion at this interface are primary mechanisms leading to particle generation and potential implant loosening.
• Understanding interface dynamics is key to interpreting retrieval data and preventing fluid ingress.

Purpose of the Study:

• To characterize the relative motions at the bore-trunnion interface of modular THRs under various loading conditions.
• To investigate the influence of taper design parameters on interface motion and contact mechanics.
• To identify motion patterns and their relationship to implant failure modes.

Main Methods:

• Development of 3D Finite Element (FE) models simulating CoCr femoral head and Ti alloy trunnion assembly.
• Inclusion of variables such as taper clearance, deviation from roundness, assembly force, and loading profiles.
• Analysis of micromotions, separation, and contact area at the bore-trunnion interface.

Main Results:

• Taper design and activity type significantly affect micromotion, separation, and contact area.
• Out-of-roundness as small as 6 μm dramatically alters contact mechanics and motion magnitude.
• A pumping motion was identified during activities like walking, jogging, and climbing stairs.
• Components of relative motion varied independently of overall motion magnitude.

Conclusions:

• High-quality manufacturing processes are essential for modular THR performance.
• Even minor deviations in trunnion geometry can substantially alter clinical outcomes.
• Interface motion characteristics are complex and influenced by multiple factors, necessitating careful design and manufacturing considerations.