Stresses in cement mantles of hip replacements: effect of femoral implant sizes, body mass index and bone quality

Abstract

The effects of femoral prosthetic heads of diameters 22 and 28 mm were investigated on the stability of reconstructed hemi-pelves with cement mantles of thicknesses 1–4 mm and different bone qualities. Materialise medical imaging package and I-Deas finite element (FE) software were used to create accurate geometry of a hemi-pelvis from CT-scan images. Our FE results show an increase in cement mantle stresses associated with the larger femoral head. When a 22 mm femoral head is used on acetabulae of diameters 56 mm and above, the probability of survivorship can be increased by creating a cement mantle of at least 1 mm thick. However, when a 28 mm femoral head is used, a cement mantle thickness of at least 4 mm is needed. Poor bone quality resulted in an average 45% increase in the tensile stresses of the cement mantles, indicating resulting poor survivorship rate.

Keywords:

• femoral implant
• cement mantle thickness
• total hip replacement
• reconstructed acetabulum
• finite element method
• bone quality

Acknowledgements

The authors acknowledge the International Society of Biomechanics, for providing a matching dissertation grant, Materialise, for the 2006 Mimics Innovation Award, and Professor John Orr for his advice.