The influence of pelvic tilt on stress distribution in the acetabulum: finite element analysis

Background Finite element analysis (FEA) has been previously applied for the biomechanical analysis of acetabular dysplasia and osteotomy. However, until now, there have been little reports on the use of FEA to evaluate the effects of pelvic tilt on stress distribution in the acetabulum. Methods We used the Mechanical Finder Ver. 7.0 (RCCM, Inc., Japan) to construct finite element models based on 3D-CT data of patients, and designed dysplasia, borderline, and normal pelvic models. For analysis, body weight was placed on the sacrum and the load of the flexor muscles of the hip joint was placed on the ilium. The pelvic tilt was based on the anterior pelvic plane, and the pelvic tilt angles were -20 degrees, 0 degrees, and 20 degrees. The load of the flexor muscle of the hip joint was calculated using the moment arm equation. Results All three models showed the highest values of von Mises stress in the -20 degrees pelvic tilt angle, and the lowest in the 20 degrees angle. Stress distribution concentrated in the load-bearing area. The maximum values of von Mises stress in the borderline at pelvic tilt angles of -20 degrees was 3.5Mpa, and in the dysplasia at pelvic tilt angles of 0 degrees was 3.1Mpa. Conclusions The pelvic tilt angle of -20 degrees of the borderline model showed equal maximum values of von Mises stress than the dysplasia model of pelvic tilt angle of 0 degrees, indicating that pelvic retroversion of -20 degrees in borderline is a risk factor for osteoarthritis of the hip joints, similar to dysplasia.