Can larger-bodied cemented femoral components reduce periprosthetic fractures? A biomechanical study

Introduction The risk for late periprosthetic femoral fractures is higher in patients treated for a neck of femur fracture compared to osteoarthritis. It has been hypothesised that osteopaenia and consequent decreased stiffness of the proximal femur are responsible for this. We investigated whether a femoral component with a bigger body would increase the torque to failure in a biaxially loaded composite Sawbone model. Materials and methods A biomechanical bone analogue was used. Two different body sizes (Exeter 44-1 versus 44-4) of a polished tapered cemented femoral stem were implanted by an experienced surgeon in seven bone analogues each and internally rotated at 40°/s until failure. Torque to fracture and fracture energy were measured using a biaxial materials testing device (Instron 8874, MI, USA). The data were non-parametric and therefore tested with the Mann–Whitney U test. Results The median torque to fracture was 156.7 Nm (IQR 19.7) for the 44-1 stem and 237.1 Nm (IQR 52.9) for the 44-4 stem ( p = 0.001). The median fracture energy was 8.5 J (IQR 7.3) for the 44-1 stem and 19.5 J (IQR 8.8) for the 44-4 stem ( p = 0.014). Conclusion The use of large body polished tapered cemented stems for neck of femur fractures increases the torque to failure in a biomechanical model and therefore is likely to reduce late periprosthetic fracture risk in this vulnerable cohort.