eCM (Eur Cell Mater / e Cells & Materials) Not-for-profit Open Access
Created by Scientists, for Scientists
 ISSN:1473-2262         NLM:100973416 (link)         DOI:10.22203/eCM

2012   Volume No 23 – pages 289-299

Title: Design, characterisation and in vivo testing of a new, adjustable stiffness, external fixator for the rat femur

Author: V Glatt, CH Evans, R Matthys

Address: Beth Israel Deaconess Medical Center, Center for Advanced Orthopaedic Studies, 330 Brookline Avenue, RN115, Boston, MA 02215, USA

E-mail: vglatt at

Key Words: External fixator; bone healing; small animal model; mechanical stiffness; mechanobiology; dynamisation

Publication date: April 21st 2012

Abstract: Very little is known about the influence of the mechanical environment on the healing of large segmental defects. This partly reflects the lack of standardised, well characterised technologies to enable such studies. Here we report the design, construction and characterisation of a novel external fixator for use in conjunction with rat femoral defects. This device not only imposes a predetermined axial stiffness on the lesion, but also enables the stiffness to be changed during the healing process. The main frame of the fixator consists of polyethylethylketone with titanium alloy mounting pins. The stiffness of the fixator is determined by interchangeable connection elements of different thicknesses. Fixators were shown to stabilise 5 mm femoral defects in rats in vivo for at least 8 weeks during unrestricted cage activity. No distortion or infections, including pin infections, were noted. The healing process was simulated in vitro by inserting into a 5 mm femoral defect, materials whose Young’s moduli approximated those of the different tissues present in regenerating bone. These studies confirmed that, although the external fixator is the major determinant of axial stiffness during the early phase of healing, the regenerate within the lesion subsequently dominates this property. There is much clinical interest in altering the mechanics of the defect to enhance bone healing. Our data suggest that, if alteration of the mechanical environment is to be used to modulate the healing of large segmental defects, this needs to be performed before the tissue properties become dominant.

Article download: Pages 289-299 (PDF file)
DOI: 10.22203/eCM.v023a22