DXA-Based Finite Element Analysis as Support for Pre and Post-operative Evaluation of Hip Arthroplasty

Purpose: Bone quality, bone density, implant type and patient anatomy are critical factors for the success of Total Hip Arthroplasty. This study aims to develop a patient-specific FE model based on DXA images to optimise preoperative planning and follow-up. Methods: Three simulations were carried out for each patient: intact femur, press-fit stem and cemented stem, selecting different prosthesis sizes and types (cemented and cementless). The loads were applied at the centre of the femoral head, whereas constraints were placed on the distal nodes of the femoral shaft to simulate the walking condition. The mechanical response was assessed through micromovements, equivalent strains and strain energy density (SED) calculation. Results: Models with press-fit prostheses show an average strain greater than 20% compared to the intact femur and 10% compared to models with cemented prostheses. Femoral average strain ranged from about 600 to about 1500 µstrains depending on the patient BMI, BMD and type of implant. The femoral prosthetic models show the highest strain values in Gruen zones located medio-proximally, and lower strains in the lateral regions, mainly for cemented implants. The SED follows the same trend as the average equivalent strain in the Gruen zones. Conclusion: DXA-based FE analysis appeared to be helpful to access bone strain distribution in prosthetic hip depending on patient anatomy, BMD, and the type of implant. The study shows the utility of equivalent strains and strains energy density in predicting bone loss and growth around the prosthesis and the influence of BMD and BMI in the final results.