Biomechanical Comparison of Periprosthetic Femoral Fracture Risk in Three Femoral Components in a Sawbone Model

The increasing use of orthopedic total hip arthroplasty implants has led to a consequent rise in the incidence of associated periprosthetic fractures (PPFs). Analysis of the National Joint Registry data showed the choice of cemented hip stem influenced the risk of a PPF occurring. However, the effect of implant design in relation to the risk of PPFs has not been investigated.

The main objective is to compare the biomechanics of PPFs as a failure of the Exeter V40, CPT, and DePuy C-Stem stems in a composite Sawbone model to identify whether a difference in the risk of fracture exists between them. Twenty-six Sawbones were divided into 3 groups, cemented with the Stryker Exeter, Zimmer CPT, or DePuy C-Stem and then torqued to fracture.

When compared with the Exeter, the CPT- and C-Stem-implanted Sawbone models would sustain PPFs at a statistically significantly lower rotation to failure (20.1° and 26.7° vs 33.6°,  P < .01) and torque to failure (124 Nm and 143 Nm vs 174 Nm,  P < .01) values. The energy release rate at failure for the Exeter was significantly higher than that for the CPT and C-Stem (61.2 Nm vs 21.8 Nm and 38.6 Nm,  P < .01), which led to more comminution.

The CPT- and C-Stem-implanted femurs, although fracturing earlier, fractured in a simple pattern with less comminution. The differences in stem design mean higher stress at the critical point of failure in the CPT implanted femur compared with the Exeter and DePuy, which is likely the reason behind the observed increased risk of PPFs with the CPT implant.