Biomechanical comparison of the pullout properties of external skeletal fixation pins in the tibiae of intact and ovariectomised ewes

B. J. Keeley; B. Heidari; N. J. Mahony; S. M. Rackard; F. J. O’Brien; T. C. Lee; O. Brennan; O. D. Kennedy; D. FitzPatrick

doi:10.3415/VCOT-07-09-0089

Veterinary and Comparative Orthopaedics and Traumatology, Table of Contents

Vet Comp Orthop Traumatol 2008; 21(05): 418-426
DOI: 10.3415/VCOT-07-09-0089

Original Research

Schattauer GmbH

Biomechanical comparison of the pullout properties of external skeletal fixation pins in the tibiae of intact and ovariectomised ewes

Authors

B. J. Keeley

¹UCD School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield, Dublin, Republic of Ireland
B. Heidari

²UCD School of Electrical, Electronic and Mechanical Engineering, Engineering and Material Sciences Centre, University College Dublin, Belfield, Dublin, Republic of Ireland
N. J. Mahony

³Trinity Centre for Bioengineering, Department of Mechanical Engineering, Trinity College, Dublin, Republic of Ireland
S. M. Rackard

¹UCD School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield, Dublin, Republic of Ireland
F. J. O’Brien

⁴Department of Anatomy, Royal College of Surgeons in Ireland, Dublin, Republic of Ireland
T. C. Lee

³Trinity Centre for Bioengineering, Department of Mechanical Engineering, Trinity College, Dublin, Republic of Ireland
O. Brennan

⁴Department of Anatomy, Royal College of Surgeons in Ireland, Dublin, Republic of Ireland
O. D. Kennedy

⁴Department of Anatomy, Royal College of Surgeons in Ireland, Dublin, Republic of Ireland
D. FitzPatrick

²UCD School of Electrical, Electronic and Mechanical Engineering, Engineering and Material Sciences Centre, University College Dublin, Belfield, Dublin, Republic of Ireland

Abstract

Summary

The pin-bone interface is the least stable component of the external skeletal fixator. Concerns exist regarding the ability to obtain adequate implant purchase in poor quality bone. Consequently, reduced bone quality has been viewed as a contra-indication for the use of external skeletal fixators. The aim of this study was to investigate the holding power of two different fixator pin designs in bone from entire and ovariectomised sheep. Thirty-two aged ewes were divided into two groups. Group 1 were controls, and Group 2 were ovariectomised (OVX). The ewes were sacrificed 12 months postovariectomy and five pairs of tibiae were harvested from each group. The holding power of cortical and cancellous fixator pins was assessed at five standardised locations on each tibia. An increase in mean cortical thickness was noted in the OVX group. The holding power of cancellous fixator pins was superior to that of cortical pins, irrespective of whether or not ovariectomy had been performed. Cancellous pins had an increased holding power in post ovariectomy bone compared to control bone. Cortical pin performance was not affected by ovariectomy. There was a lack of correlation between the incidence of insertional fractures of the far cortex and implant holding power. The results raise questions over the effectiveness of ovariectomy in establishing osteopaenic bone suitable for assessing implant performance, hence further investigations are warranted.

Keywords

Implant - holding power - mechanical properties - cortical - cancellous

Full Text

References

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