Stress analysis of total hip arthroplasty with a fully hydroxyapatite-coated stem: comparing thermoelastic stress analysis and CT-based finite element analysis.

Purpose: The aim of this study was to evaluate the stress distribution in a synthetic femur that was implanted with a fully hydroxyapatite-coated stem using thermoelastic stress and finite element analyses, and to clarify the differences in the stress distributions between these two methods.

Methods: Thermoelastic stress analysis is a stress-analysis technique that employs the thermoelastic effect. Sinusoidal vertical loads were applied to the head of the stem placed on the synthetic femur, and surface stress distribution images were acquired using an infrared stress measurement system. The finite element model for the synthetic femur and stem were set up similarly to the thermoelastic stress analysis experiment, and vertical load was applied to the head of the stem. Surface stress distribution and stress values obtained via these two methods were compared.

Results: Thermoelastic stress analysis showed that compressive and tensile stresses were distributed from the proximal femur to the diaphysis, not only on the medial and lateral surfaces, but also on the anterior and posterior surfaces. However, finite element analysis showed that compressive stress was not distributed on the anterior and posterior surfaces of the femoral intertrochanter. The stress values of thermoelastic stress analysis tended to be higher in the proximal femur than that obtained via the finite element analysis.

Conclusions: The surface stress distribution obtained by these two methods were different specifically in the proximal femur. Our results imply that thermoelastic stress analysis has a better potential than finite element analysis to show the surface stress distribution that reflects the stem design.