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Research: A. J. Metcalfe, M. Saleh, and L. Yang Techniques for improving stability in oblique fractures treated by circular fixation with particular reference to the sagittal plane J Bone Joint Surg Br 2005; 87-B: 868-872 [Abstract] [Full text] [PDF]

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Response to Alemdaroglu et al

Lang Yang, Andrew Metcalfe   (26 October 2005)

Letter from Alemdaroğlu, İltar, Atlihan and Kara

Bahadır Alemdaroğlu, Serkan İltar, Doğan Atlıhan, Talip Kara   (5 October 2005)

Response to Alemdaroglu et al 26 October 2005
Lang Yang University of Sheffield, Andrew Metcalfe Send letter to journal: Re: Response to Alemdaroglu et al L.Yang{at}sheffield.ac.uk Lang Yang, et al.	Sir, We thank Drs. B. Alemdaroglu et al for their interest in our paper and for their comments. We agree that torsional loading may be important in generating shear movement at the fracture site for a spiral fracture and the arched wires may be useful to reduce this component of inter-fragmentary shear movement. It is difficult to comment on the relative importance of torsional and axial shear stresses in spiral fractures in vivo, or the use of additional fixation methods, without specifically testing a spiral fracture model. Our initial experience with olive wires in fractures where the obliquity is seen in the coronal plane (i.e. where an olive wire could be safely be placed medio-laterally) implied that they improved healing.1 We did not have the facility to perform torsional tests on our Sawbones models. In loading the models in axial compression and combined compression and bending, we believed our testing gave a reasonable estimation of the major loading conditions in the tibia for walking. We would like to sound a caution in interpreting the results of mechanical testing. Fleming et al tested models with a transverse fracture, as do the majority of studies which examine the mechanics of external fixation. Due to the differences in fracture geometry and forces generated by contact between bony fragments, the results cannot be translated directly to either oblique or spiral fractures. For example, an axial displacement in a transverse fracture will transform into a shear displacement and compression in an oblique fracture, simply because of the obliquity. The majority of fracture fixation studies utilise gap models, in which the contact between bony fragments does not occur at all. We thank Dr Alemdaroğlu et al for pointing out the error in the legend to Figure 1, for which we apologise. A.Metcalfe MBChB BMedSc L.Yang PhD Reference: 1. Metcalfe AJ, Branfoot T, Shelbrooke K, Oleksak M, Saleh M. Tibial fractures treated with circular fixation: does the use of olive wires at the fracture site improve healing? Injury 2003;34:145-9.
Letter from Alemdaroğlu, İltar, Atlihan and Kara 5 October 2005
Bahadır Alemdaroğlu, MD Ankara Education and Research Hospital, Ankara, Turkey, Serkan İltar, Doğan Atlıhan, Talip Kara Send letter to journal: Re: Letter from Alemdaroğlu, İltar, Atlihan and Kara balemdaroglu{at}yahoo.com.tr Bahadır Alemdaroğlu, et al.	Sir, We read this article with interest. This is detailed research which investigates how to reduce the shear force in oblique fractures. We agree that most of the nonunions of the tibia treated by circular external fixators are cases exposed to axial shear forces instead of axial compression. Oblique fractures with an angle of more than 45° are mostly spiral fractures. The torsional shear forces may play a major role in these fractures in practice. Unfortunately, the authors did not differentiate between axial shear forces, bending shear forces and torsional shear forces. Fleming et al1 found that olive wires increase bending shear stiffness, but not the torsional stiffness. The arched wires would be particularly expected to resist the torsional shear forces and indirectly to the A-P plane shear forces. We should also indicate that the legends of Figure 1c and Figure 1e should be transposed. B. ALEMDAROGLU, MD S. ILTAR, MD D. ATLIHAN, MD T. KARA, MD Ankara Education and Research Hospital, Ankara, Turkey. 1. Fleming B, Paley D, Kristiansen T, Pope M. A biomechanical analysis of the Ilizarov external fixator. Clin Orthop Relat Res 1989;241:95-105.