Evaluation of the effect of stem alignment on femoral mechanical stress using simulation models of cemented total hip arthroplasty: A finite element study.

Abstract

This study investigated the effects of cemented stem alignment on the femoral mechanical stress in total hip arthroplasty (THA) simulation models using finite element analysis (FEA) and verified whether only the commonly used von Mises equivalent stress was sufficient for evaluating mechanical stress. We performed 20 consecutive THAs using collarless, polished, tapered, and cemented stems for the Dorr classification type B of osteoarthritis in March 2022. Simulation models were created using three-dimensional imaging software using postoperative computed tomography data. Under malalignment conditions, the rate of mechanical stress change for each Gruen zone was calculated using FEA. Mechanical stress was classified into von Mises equivalent, maximum principal, and minimum principal stresses. In the anterolateral view, the rates of change in all mechanical stresses showed no significant difference between the neutral and malalignment positions. In the lateral view, however, the rates of change in the maximum principal stress at zone 12 and the minimum principal stress at zones 9 and 10 significantly differed between the neutral and flexed positions. Stress mapping revealed that the maximum principal stresses tended to be high in zones 2 and 3, whereas the minimum principal stresses tended to be high in zones 5 and 6. The locations and magnitudes of stress concentrations varied depending on the stress type-von Mises equivalent, maximum principal, or minimum principal stress. FEA showed that the flexion in cemented stems increases the maximum and minimum principal stresses and should therefore be avoided. Additionally, evaluating only the von Mises equivalent stress is insufficient for fully assessing the mechanical stress acting on the femur.