Taper-Trunnion Interface Stress Varies Significantly With Head Size and Activity

Area of Science:

• Biomedical Engineering
• Orthopedic Surgery
• Materials Science

Background:

• Total hip arthroplasty (THA) utilizes modular components, commonly a femoral stem with a Morse taper and a femoral head.
• Increased use of larger (≥36 mm) femoral heads aims to reduce dislocation rates but has been linked to clinical failures.
• Mechanically assisted crevice corrosion at the head-stem taper junction is a cause for revision surgery.

Purpose of the Study:

• To investigate the relationship between femoral head size and trunnion stress in THA.
• To analyze the impact of geometric parameters like horizontal lever arm (HLA) and trunnion load offset on trunnion stresses.
• To test the hypothesis that increasing head size and HLA elevate trunnion stress.

Main Methods:

• Finite element analysis (FEA) was employed to model a titanium hip stem and cobalt-chromium femoral heads.
• Simulations were conducted using four commercially available head sizes and four distinct physiological loading conditions.
• The study focused on evaluating stress distribution within the trunnion under various simulated conditions.

Main Results:

• Trunnion stress was found to increase with larger femoral head sizes.
• Increased horizontal lever arm (HLA) and trunnion load offset significantly elevated trunnion stresses.
• Exceptionally high trunnion stresses were observed under specific loading scenarios, particularly with larger head diameters.

Conclusions:

• Larger femoral head sizes in THA are associated with increased trunnion stress.
• Design considerations should aim to mitigate high stresses, especially under challenging physiological loads.
• Avoiding larger head sizes may be beneficial in reducing the risk of implant failure due to taper junction stress.