Investigation of factors affecting loosening of ilizarov ring-wire external fixator systems at the bone-wire interface

• Published in: Journal of orthopaedic research 2012-05, Vol.30 (5), p.726-732
• Main Authors: Donaldson, Finn E., Pankaj, Pankaj, Simpson, A. Hamish R.W.
• Format: Article
• Language: English
• Subjects: aging; Bone Wires - adverse effects; bone yielding; Equipment Failure; External Fixators - adverse effects; Female; finite element analysis; fracture fixation; Fracture Fixation - adverse effects; Humans; wire pre-tension
• ISSN: 0736-0266; 1554-527X
• DOI: 10.1002/jor.21587

The potential for peri‐implant bone yielding and subsequent loosening of Ilizarov ring‐wire external fixation systems was investigated using non‐linear finite element (FE) analyses. A strain‐based plasticity model was employed to simulate bone yielding. FE models also incorporated contact behavior at the wire‐bone interface, orthotropic elasticity, and periosteal‐endosteal variation of bone properties. These simulations were used to determine the extent and location of yielding with change in age‐related bone structure and properties for the bone‐Ilizarov construct at the tibial midshaft. At critical wire‐bone interfaces, the predicted volume of yielded bone with four wires (on either side of the fracture) was ∼40% of that with two wires. Old‐aged cases showed considerably greater bone yielding at the wire‐bone interface than young cases (1.7–2.2 times greater volumes of yielded bone). The volume of yielded bone at all wire‐bone interfaces decreased with an increase in wire pre‐tension. The absence of continuous through‐thickness yielding offers an explanation for the clinical observation that Ilizarov ring‐wire fixation can provide stable fracture fixation even in bone with high porosity. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:726–732, 2012