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


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).


CONCLUSIONS
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.
Institute of Health and Biomedical Innovation, Queensland University of Technology, The Prince Charles Hospital, Chermside, Brisbane, QLD, 4032, Australia.
Bastiaan L
BL
Ginsel
Takkan
T
Morishima
Lance J
LJ
Wilson
Sarah L
SL
Whitehouse
Ross W
RW
Crawford
D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D001696:Biomechanical Phenomena; D005264:Femoral Fractures / Q000503:physiopathology / Q000601:surgery*; D006621:Hip Joint / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D057068:Periprosthetic Fractures / Q000503:physiopathology / Q000517:prevention & control*; D016059:Range of Motion, Articular; D019415:Torque