Short communication A biomechanical comparison of composite femurs and cadaver femurs used in experiments on operated hip fractures Trude Basso a,b,n , Jomar Klaksvik a , Unni Syversen c,d , Olav A. Foss a,b Q1 a Orthopaedic Research Centre, Department of Orthopaedics, St. Olav’s University Hospital, Trondheim, Norway b Department of Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway c Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway d Department of Endocrinology, St. Olav’s University Hospital, Trondheim, Norway article info Article history: Accepted 17 October 2014 Keywords: Hip fracture Cadaver bone Composite bone Fracture fixation Strain Biomechanics abstract Fourth generation composite femurs (4GCFs, models #3406 and #3403) simulate femurs of males o80 years with good bone quality. Since most hip fractures occur in old women with fragile bones, concern is raised regarding the use of standard 4GCFs in biomechanical experiments. In this study the stability of hip fracture fixations in 4GCFs was compared to human cadaver femurs (HCFs) selected to represent patients with hip fractures. Ten 4GCFs (Sawbones, Pacific Research Laboratories, Inc., Vashon, WA, USA) were compared to 24 HCFs from seven females and five males 460 years. Proximal femur anthropometric measurements were noted. Strain gauge rosettes were attached and femurs were mounted in a hip simulator applying a combined subject-specific axial load and torque. Baseline measurements of resistance to deformation were recorded. Standardized femoral neck fractures were surgically stabilized before the constructs were subjected to 20,000 load-cycles. An optical motion tracking system measured relative movements. Median (95% CI) head fragment migration was 0.8 mm (0.4 to 1.1) in the 4GCF group versus 2.2 mm (1.5 to 4.6) in the cadaver group (p ¼0.001). This difference in fracture stability could not be explained by observed differences in femoral anthropometry or potential overloading of 4GCFs. 4GCFs failed with fracture-patterns different from those observed in cadavers. To conclude, standard 4GCFs provide unrealistically stable bone-implant constructs and fail with fractures not observed in cadavers. Until a validated osteopenic composite femur model is provided, standard 4GCFs should only be used when representing the biomechanical properties of young healthy femurs. & 2014 Published by Elsevier Ltd. 1. Introduction Most hip fractures are fragility fractures occurring in old individuals (Parker and Johansen, 2006). These fractures require surgical stabilization (Parker and Handoll, 2010; Parker and Stockton, 2001). Laboratory studies on fracture fixating implants are conducted to better understand their effects on the fractured bone and also to explore new designs before clinical introduction (Basso et al., 2012). Traditionally, HCFs have been used for ex vivo biomechanical studies. Factors like availability of donors, rapid material break- down (Cartner et al., 2011), large variability in anthropometry and mechanical properties, as well as ethical considerations make the use of HCFs troublesome. Consequently, artificial femurs have been welcomed by the biomechanical community (Cristofolini et al., 1996; Zdero et al., 2008). One of the most used composite femur model on the market is made of fiberglass-reinforced epoxy and polyurethane foam simulating cortical and cancellous bone respectively (Sawbones, Pacific Research Laboratories, Inc., Vashon, WA, USA). The standard large and medium 4th generation composite femurs (4GCFs, models #3406 and #3403) available by order from the manufacturer’s catalog, are modeled to represent femurs of healthy males o80 years of age with good bone quality (Gardner et al., 2010). Previous studies have shown adequate results when comparing the mechanical properties of whole- bone 4GCFs to HCFs (Gardner et al., 2010; Heiner, 2008). 4GCFs were also found to be good analogs to HCFs regarding pull-out strength of bone screws, (Zdero et al., 2008, 2007) although this finding was questioned in a later study (Topp et al., 2012). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com Journal of Biomechanics http://dx.doi.org/10.1016/j.jbiomech.2014.10.025 0021-9290/& 2014 Published by Elsevier Ltd. n Corresponding author at: Orthopaedic Research Centre, Department of Ortho- paedics, St. Olav’s University Hospital, Postboks 3250 Sluppen, Trondheim 7006, Norway. Tel.: þ47 72 82 60 00; fax: þ47 72 82 60 33, Mobile: þ47 95 24 19 82. E-mail address: trude.basso@ntnu.no (T. Basso). Please cite this article as: Basso, T., et al., A biomechanical comparison of composite femurs and cadaver femurs used in experiments on operated hip fractures. Journal of Biomechanics (2014), http://dx.doi.org/10.1016/j.jbiomech.2014.10.025i Journal of Biomechanics ∎ (∎∎∎∎) ∎∎∎–∎∎∎