Todd Stewart

Postoperative periprosthetic femoral fracture following hip replacement has been the subject of many varied experimental approaches. Cadaveric samples offer realistic fit and fracture patterns but are subject to large between-sample variation. Composite femurs have not yet been validated for this purpose. We compared the results of composite femurs to cadaveric femurs using an established methodology. In vitro postoperative periprosthetic fracture results using axial-rotational loading were compared between 12 composite femurs and nine fresh frozen femurs, which were implanted with an otherwise identical collarless (6 composite vs 4 cadaveric) or collared (6 composite vs 5 cadaveric) cementless femoral stem using identical methodology. Fracture torque and rotational displacement were measured and torsional stiffness and rotational work prior to fracture were estimated. Fractures patterns were graded according to the Unified Classification System. Fracture torque, displacement, torsional stiffness and fracture patterns for cadaveric and composite femurs were similar between groups. There was a trend for a greater rotational displacement in the cadaveric groups, which lead to a decrease in torsional stiffness and a significantly greater rotational work prior to fracture for all cadaveric specimens (collarless stems: 10.51 [9.71 to 12.57] vs 5.21 [4.25 to 6.04], p = 0.01 and for collared stems: 15.38 [14.01 to 17.05] vs 5.76 [4.92 to 6.64], p = 0.01). Given comparable fracture torque and the similarity in fracture patterns for fracture trials using composite samples versus cadaveric femurs, the use of composite femur models may be a reasonable choice for postoperative periprosthetic femoral fracture studies within certain limitations.