MedicalEngineering&Physics26(2004)93–108 www.elsevier.com/locate/medengphy Finite element analysis of a femoral retrograde intramedullary nail subjecttogaitloading G.Cheung b,e ,P.Zalzal c ,M.Bhandari d ,J.K.Spelt b ,M.Papini a, a Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, Ont., Canada M5B 2K3 b Department of Mechanical and Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, Ont., Canada M5S 3G8 c Division of Orthopaedic Surgery, Mount Sinai Hospital, 600 University Avenue, Suite 476A, Toronto, Ont., Canada M5G 1X5 d Department of Clinical Epidemiology and Biostatistics, McMaster Health Sciences Centre, Room 2C3, 1200 Main Street West, Hamilton, Ont., Canada L8N 3Z5 e University of Toronto, Institute of Biomaterials and Biomedical Engineering, Rosebrugh Building, 4 Taddle Creek Road, Toronto, Ont., Canada M5S 3G9 Received4March2003;receivedinrevisedform30July2003;accepted3October2003 Abstract Intramedullary nails are routinely used in the treatment of fractures of the femur. While their eﬀectiveness has been demon- strated clinically, a number of complications, including bone refracture and implant failure, persist. This paper presents novel three-dimensional ﬁnite element (FE) models, at four stages of gait, of: (i) a realistic femur analogue known as third generation composite bone, and (ii) a system consisting of an intramedullary nail implanted in the femur of (i). A comparison of experimen- tally measured strains on the surface of the femur with those predicted by the FE model revealed good agreement. The models were then used to identify implant/bone load sharing patterns, and areas of stress concentration in both the intramedullary nail and the bone, when statically locked by one or two screws at either end. The results of this study can be used to guide future implant design and surgical procedure. # 2003IPEM.PublishedbyElsevierLtd.Allrightsreserved. Keywords: Biomechanics;Intramedullarynail;Finiteelementanalysis;Femur;Stress;Fractureﬁxation 1. Introduction Intramedullary nails are implants placed within the intramedullary canal of a bone to stabilize long bone fractures. They also maintain alignment of the fracture ends while healing occurs, and (in the dynamised con- ﬁguration) allow load transfer to occur across the frac- ture. The success of intramedullary nails in the treatment of femoral fractures has maintained them as the gold standard implant for such injuries. However, complications still exist, including: failure or bending of the locking screws [1–3], loosening of the locking screws [2], failure of the nail through the screw hole [2,4], and bone refracture at the end of the nail or through the screw holes [5,6].Inaddition,thewidevar- iety of nail designs and conﬁgurations available to the surgeon has resulted in some confusion as to which implantisbestsuitedforaparticularfracture. Some suggested explanations for these failures, both in the bone and in the implant, include: high stress concentration in certain regions, torsional deformity, and stress shielding, in which the bone sees a reduced level of stress than it would normally (i.e. without the implant present) because it is much less stiﬀ than the metal implant. This reduced level of stress can result in a weakened bone, a phenomenon attributed to Wolﬀ’s Law [7], which holds that bone remodels in response to reduced applied stress and strain levels. Unfortunately, the detailed load sharing between bone and nail, and thelocationsofhighstressconcentrationinresponseto realistic loading and conﬁguration of the screws,  Corresponding author. Tel.: +1-416-979-5000x7655; fax: +1-416- 979-5265. E-mail address: mpapini@ryerson.ca (M. Papini). 1350-4533/$-seefrontmatter # 2003IPEM.PublishedbyElsevierLtd.Allrightsreserved. doi:10.1016/j.medengphy.2003.10.006