Attempts to preserve periacetabular bone stock following total hip replacement have largely ignored the potential for stress shielding in the acetabulum. We sought to quantify the change in stress distribution in acetabular bone with components of varying material stiffness by developing a high-resolution 3-D finite element model from CT scans of a young female donor. Periprosthetic bone stresses and strains on the left pelvis were compared with hemispherical cups of various material properties and with a horseshoe shaped polymeric design described in the recent literature. We observed unphysiologic periacetabular bone stress and strain fields for all designs tested. For hemispherical components, reduction of the acetabular shell material modulus caused modest changes in bone stress compared to the changes in implant geometry. The horseshoe shaped cup more effectively loaded the acetabular structures than the hemispherical design. Our results suggest stress and strain fields in pelvic structures after introduction of hemispherical acetabular components predict inevitable bone adaptation that cannot be resolved by changes in implant material properties alone. Radical changes in implant design may be necessary for long term maintenance of supporting structures in the reconstructed acetabulum.
From *Stryker Orthopaedics, Mahwah, NJ; †Exponent Inc, Philadelphia, PA; and ‡School of Biomedical Engineering, Science & Health Systems, Drexel University, Philadelphia, PA.
One or more of the authors (KLO and SMK) have received funding from Stryker Orthopaedics, Mahwah, NJ.
Each author certifies that his or her institution has approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.
Correspondence to: Michael T. Manley, PhD, Academic Director, Homer Stryker MD Center for Orthopaedic Education and Clinical Research, 325 Corporate Drive, Mahwah, NJ 07430. Phone: 201-248-5508; Fax: 201-831-4885; E-mail: firstname.lastname@example.org.