Failure Analysis of the Wire Fixation Bolts of an Ilizarov External Fixator
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TECHNICAL ARTICLE—PEER-REVIEWED
Failure Analysis of the Wire Fixation Bolts of an Ilizarov External Fixator P. C. Ortega • W. B. Medeiros Jr. • E. Rosa • R. Amorim • G. Cardoso L. N. Matos • C. R. M. Roesler
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Submitted: 9 September 2014 / Accepted: 13 October 2014 / Published online: 7 November 2014 Ó ASM International 2014
Abstract The Ilizarov method is a treatment used to recover the functionality of the upper and lower limbs of patients who have lost bone tissues due to fractures or/and infections caused by accidents or congenital problems. This technique consists of assembling a device on the patient’s limb through which the bone is manipulated gradually. The device consists of external rings connected to each other by threaded rods and fixed to the bone by small diameter steel wires. These wires fasten the bone in an axial cross through a central axis perpendicular to the plane of the bone end and they are tightened to the rings by fixation bolts to provide assembly stability. The proper operation of the device depends mainly on the wire tension, which, in turn, depends on the torque applied to the bolts that hold the wires in place. The failure of these wire fixation bolts may compromise the Ilizarov frame function. In this study, four slotted bolts from a series of slotted bolts fractured during the assembly of Ilizarov fixator in clinical practice were analyzed and the upper limit for tightening these bolts was investigated. The results show that the failures occurred through a combination of mechanical and microstructural factors, including stress concentrators at the upper region of the screw, a high level of microstructural inclusions, and P. C. Ortega (&) W. B. Medeiros Jr. C. R. M. Roesler Laborato´rio de Engenharia Biomecaˆnica (LEBm), Hospital Universita´rio, Universidade Federal de Santa Catarina, Floriano´polis, SC 88040-900, Brazil e-mail: [email protected] E. Rosa GRANTE, Depto. Engenharia Mecaˆnica, Universidade Federal de Santa Catarina, Floriano´polis, SC 88040-900, Brazil R. Amorim G. Cardoso L. N. Matos Hospital Celso Ramos, Secretaria de Sau´de de Santa Catarina, Floriano´polis, SC 88040-900, Brazil
poor surface finish. The mechanical behavior of the bolts under loads was analyzed using the finite element method with the purpose of correlating it with the failure of the bolts. Keywords Ilizarov external fixator Wire fixation bolts Slotted bolt failure
Introduction The Ilizarov system is a frame device developed by Gravriil Ilizarov in Kurgan, Siberia, in 1952. It is used in a specific orthopedic method of external bone fixation. This method relies on the principle of axial compressive loads and micro-movements in the osteogenic zone stimulating biological bone bridging of the fracture gap [1–5]..This explains the success of the Ilizarov system and the reason why it succeeds when other more rigid techniques have failed. The assembly of the Ilizarov system consists of external rings connected to each other by threaded rods and steel wires and/or pins o
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