Research Article| Volume 43, ISSUE 10, P1764-1770, October 2012

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Bone properties affect loosening of half-pin external fixators at the pin–bone interface

  • Finn E. Donaldson
    School of Engineering, The University of Edinburgh, Edinburgh, UK

    Edinburgh Orthopaedic Engineering Centre, The University of Edinburgh, Edinburgh, UK
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  • Pankaj Pankaj
    Corresponding author at: School of Engineering, The University of Edinburgh, Alexander Graham Bell Building, The King's Buildings, Edinburgh EH9 3JL, UK. Tel.: +44 131 650 5800; fax: +44 131 650 6781.
    School of Engineering, The University of Edinburgh, Edinburgh, UK

    Edinburgh Orthopaedic Engineering Centre, The University of Edinburgh, Edinburgh, UK
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  • A. Hamish R.W. Simpson
    Edinburgh Orthopaedic Engineering Centre, The University of Edinburgh, Edinburgh, UK

    Department of Orthopaedic Surgery & Trauma, The University of Edinburgh, Edinburgh, UK
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      Local bone yielding at the pin–bone interface of external fixation half-pins has been known to initiate fixator loosening. Deterioration of bone properties due to ageing and disease can lead to an increase in the risk of pin loosening. This study determines the extent, locations and mechanics of bone yielding for unilateral external fixation systems at the tibial midshaft with changes in age-related bone structure and properties. The study also evaluates the effect of the number of pins used in the fixation system and use of titanium pins (in place of steel) on bone yielding.


      We employ nonlinear finite element (FE) simulations. Strain-based plasticity is used to simulate bone yielding within FE analyses. Our analyses also incorporate contact behaviour at pin–bone interfaces, orthotropic elasticity and periosteal–endosteal variation of bone properties.


      The results show that peri-implant yielded bone volume increases by three times from young to old-aged cases. The use of three, rather than two half-pins (on either side of the fracture), reduces the volume of yielded bone by 80% in all age groups. The use of titanium half-pins resulted in approximately 60–65% greater volumes of yielded bone.


      We successfully simulate half-pin loosening at the bone–implant interface which has been found to occur clinically. Yielding across the full cortical thickness may explain the poor performance of these devices for old-aged cases. The models are able to identify patients particularly at risk of half-pin loosening, who may benefit from alternative fixator configurations or techniques such as those using pre-tensioned fine wires.


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        • Chao E.Y.S.
        • Hein T.J.
        Mechanical performance of standard Orthofix external fixator.
        Orthopedics. 1988; 11: 1057-1069
        • Behrens F.
        General theory and principles of external fixation.
        Clinical Orthopaedics and Related Research. 1989; 241: 15-23
        • Aro H.T.
        • Markel M.D.
        • Chao E.Y.S.
        Cortical bone reactions at the interface of external fixation half-pins under different loading conditions.
        The Journal of Trauma. 1993; 35: 776-785
        • Pettine K.A.
        • Chao E.Y.S.
        • Kelly P.J.
        Analysis of the external fixator pin–bone interface.
        Clinical Orthopaedics and Related Research. 1993; 293: 18-27
        • Wikenheiser M.A.
        • Markel M.D.
        • Lewallen D.G.
        • Chao E.Y.S.
        Thermal response and torque resistance of five cortical half-pins under simulated insertion technique.
        Journal of Orthopaedic Research. 1995; 13: 615-619
        • Goslings J.C.
        External fixation in osteoporotic bone.
        in: Yuehuei H.A. Internal fixation in osteoporotic bone. Thieme, New York2002: 186-193
        • Huiskes R.
        • Chao E.Y.S.
        • Crippen T.E.
        Parametric analyses of pin–bone stresses in external fracture fixation devices.
        Journal of Orthopaedic Research. 1985; 3: 341-349
        • Clifford R.P.
        • Lyons T.J.
        • Webb J.K.
        Complications of external fixation of open fractures of the tibia.
        Injury. 1987; 18: 174-176
        • Parameswaran A.D.
        • Roberts C.S.
        • Seligson D.
        • Voor M.
        Pin tract infection with contemporary external fixation: how much of a problem?.
        Journal of Orthopaedic Trauma. 2003; 17: 503-507
        • Currey J.D.
        Changes in the impact energy absorption of bone with age.
        Journal of Biomechanics. 1997; 12: 459-469
        • Donaldson F.E.
        • Pankaj P.
        • Cooper D.M.L.
        • Thomas C.D.L.
        • Clement J.G.
        • Simpson A.H.R.W.
        Relating age and micro-architecture with apparent-level elastic constants: A μFE study of female cortical bone from the anterior femoral midshaft.
        Proceedings of the Institution of Mechanical Engineers – Part H: Journal of Engineering in Medicine. 2011; 225: 585-596
        • Giannoudis P.V.
        • Schneider E.
        Principles of fixation of osteoporotic fractures.
        The Journal of Bone and Joint Surgery (British). 2006; 88-B: 1272-1278
        • Russo C.R.
        • Lauretani F.
        • Seeman E.
        • Bartali B.
        • Bandinelli S.
        • Di Iorio A.
        • et al.
        Structural adaptations to bone loss in aging men and women.
        Bone. 2006; 38: 112-118
        • Chao E.Y.S.
        • Kasman R.A.
        • An K.N.
        Rigidity and stress analyses of external fracture fixation devices – a theoretical approach.
        Journal of Biomechanics. 1982; 15: 971-983
        • Huiskes R.
        • Chao E.Y.S.
        Guidelines for external fixation frame rigidity and stresses.
        Journal of Orthopaedic Research. 1986; 4: 68-75
        • Juan J.A.
        • Prat J.
        • Vera P.
        • Hoyos J.V.
        • Sanchez-Lacuesta J.
        • Peris J.L.
        • et al.
        Biomechanical consequences of callus development in Hoffmann, Wagner, orthofix and Ilizarov external fixators.
        Journal of Biomechanics. 1992; 25: 995-1006
        • Oni O.O.A.
        • Capper M.
        • Soutis C.
        A finite element analysis of the effect of pin distribution on the rigidity of a unilateral external fixation system.
        Injury. 1993; 24: 525-527
        • Burgers P.T.P.W.
        • Van Riel M.P.J.M.
        • Vogels L.M.M.
        • Stam R.
        • Patka P.
        • Van Lieshout E.M.M.
        Rigidity of unilateral external fixators – a biomechanical study.
        Injury. 2011; 42: 1449-1454
        • Donaldson F.E.
        • Pankaj P.
        • Simpson A.H.R.W.
        Investigation of factors affecting loosening of Ilizarov ring-wire external fixator systems at the bone–wire interface.
        Journal of Orthopaedic Research. 2012; 30: 726-732
        • Karunratanakul K.
        • Schrooten J.
        • Van Oosterwyck H.
        Finite element modelling of a unilateral fixator for bone reconstruction: Importance of contact settings.
        Medical Engineering and Physics. 2010; 32: 461-467
        • Shahar R.
        • Shani Y.
        Fracture stabilization with type II external fixator vs. type I external fixator with IM pin.
        Veterinary and Comparative Orthopaedics and Traumatology. 2004; 17: 91-96
        • Cowin S.C.
        • Mehrabadi M.M.
        Identification of the elastic symmetry of bone and other materials.
        Journal of Biomechanics. 1989; 22: 503-515
        • Cifuentes A.O.
        • Kalbag A.
        A performance study of tetrahedral and hexahedral elements in 3-D finite element structural analysis.
        Finite Elements in Analysis and Design. 1992; 12: 313-318
        • Cowin S.C.
        • Yang G.
        Averaging anisotropic elastic constant data.
        Journal of Elasticity. 1997; 46: 151-180
        • Ebacher V.
        • Tang C.
        • McKay H.
        • Oxland T.R.
        • Guy P.
        • Wang R.
        Strain redistribution and cracking behaviour of human bone during bending.
        Bone. 2007; 40: 1265-1275
        • Mercer C.
        • He M.Y.
        • Wang R.
        • Evans A.G.
        Mechanisms governing the inelastic deformation of cortical bone and application to trabecular bone.
        Acta Biomaterialia. 2006; 2: 59-68
        • Bayraktar H.H.
        • Morgan E.F.
        • Niebur G.L.
        • Morris G.E.
        • Wong E.K.
        • Keaveny T.M.
        Comparison of the elastic and yield properties of human femoral trabecular and cortical bone tissue.
        Journal of Biomechanics. 2004; 37: 27-35
        • Gefen A.
        Optimizing the biomechanical compatibility of orthopedic screws for bone fracture fixation.
        Medical Engineering and Physics. 2002; 24: 337-347
        • Zanetti E.M.
        • Salaorno M.
        • Grasso G.
        • Audenino A.L.
        Parametric analysis of orthopedic screws in relation to bone density.
        The Open Medical Informatics Journal. 2009; 3: 19-26
        • Lim T.-H.
        • Eck J.C.
        • An H.
        • Hong J.H.
        • Ahn J.-Y.
        • You J.W.
        Biomechanics of transfixation in pedicle screw instrumentation.
        Spine. 1996; 21: 2224-2229
        • Chen S.I.
        • Lin R.M.
        • Chang C.H.
        Biomechanical investigation of pedicle screw–vertebrae complex: a finite element approach using bonded and contact interface conditions.
        Medical Engineering and Physics. 2003; 25: 275-282
        • Currey J.D.
        The many adaptations of bone.
        Journal of Biomechanics. 2003; 36: 1487-1495
        • Ali A.M.
        • Burton M.
        • Hashmi M.
        • Saleh M.
        Treatment of displaced bicondylar tibial plateau fractures (OTA-41C2&3) in patients older than 60 years of age.
        Journal of Orthopaedic Trauma. 2003; 17: 346-352
        • Board T.N.
        • Yang L.
        • Saleh M.
        Why fine-wire fixators work: an analysis of pressure distribution at the wire–bone interface.
        Journal of Biomechanics. 2007; 40: 20-25
        • Weaver J.K.
        • Chalmers J.
        Cancellous bone: its strength and changes with aging and an evaluation of some methods for measuring its mineral content.
        The Journal of Bone and Joint Surgery (American). 1966; 48-A: 289-298
        • Wu J.J.
        • Shyr H.S.
        • Chao E.Y.
        • Kelly P.J.
        Comparison of osteotomy healing under external fixation devices with different stiffness characteristics.
        The Journal of Bone and Joint Surgery (American). 1984; 66: 1258-1264
        • Williams E.A.
        • Rand J.A.
        • An K.N.
        • Chao E.Y.
        • Kelly P.J.
        The early healing of tibial osteotomies stabilized by one-plane or two-plane external fixation.
        The Journal of Bone and Joint Surgery (American). 1987; 69: 355-365
        • Cunningham J.L.
        • Evans M.
        • Kenwright J.
        Measurement of fracture movement in patients treated with unilateral external skeletal fixation.
        Journal of Biomedical Engineering. 1989; 11: 118-122
        • Kershaw C.
        • Cunningham J.L.
        • Kenwright J.
        Tibial external fixation, weight bearing and fracture movement.
        Clinical Orthopaedics and Related Research. 1993; 293: 28-36
        • Vijayakumar V.
        • Marks L.
        • Bremmer-Smith A.
        • Hardy J.
        • Gardener T.
        Load transmission through a healing tibial fracture.
        Clinical Biomechanics. 2006; 21: 49-53