Axial forces and bending moments in the loaded rabbit tibia in vivo

Janin Reifenrath,Andrea Meyer-Lindenberg,Nina Angrisani,Silke Besdo,Daniel Gottschalk

doi:10.1186/1751-0147-54-21

Abstract

BackgroundDifferent animal models are used as fracture models in orthopaedic research prior to implant use in humans, although biomechanical forces can differ to a great extend between species due to variable anatomic conditions, particularly with regard to the gait. The rabbit is an often used fracture model, but biomechanical data are very rare. The objective of the present study was to measure axial forces, bending moments, and bending axis directly in the rabbit tibia in vivo. The following hypothesis was tested: Axial forces and bending moments in the mid-diaphysis of rabbit tibia differ from other experimental animals or indirectly calculated data.MethodsA minifixateur system with 4 force sensors was developed and attached to rabbit tibia (n = 4), which were subsequently ostectomised. Axial forces, bending moments and bending angles were calculated telemetrically during weight bearing in motion between 6 and 42 days post operation.ResultsHighest single values were 201% body weight [% bw] for axial forces and 409% bw cm for bending moments. Whereas there was a continous decrease in axial forces over time after day 10 (P = 0.03 on day 15), a decrease in bending moments was inconsistent (P = 0.03 on day 27). High values for bending moments were frequently, but not consistently, associated with high values for axial forces.ConclusionAxial forces in rabbit tibia exceeded axial forces in sheep, and differed from indirectly calculated data. The rabbit is an appropriate fracture model because axial loads and bending moments in rabbit tibia were more closely to human conditions than in sheep tibia as an animal model.

Highlights

Different animal models are used as fracture models in orthopaedic research prior to implant use in humans, biomechanical forces can differ to a great extend between species due to variable anatomic conditions, with regard to the gait
Bone remodelling, gait, and the biomechanical forces acting on the bones differ presumably from those of humans, screening of newly developed implant materials is common in animal
Direct measurement methods using external fixateur systems are apparently only described for humans [16,17] and sheep [11,12,13], but these systems were not small enough to be adapted to the rabbit tibia

Summary

Introduction

Different animal models are used as fracture models in orthopaedic research prior to implant use in humans, biomechanical forces can differ to a great extend between species due to variable anatomic conditions, with regard to the gait. In comparison to calculated loads in human mid diaphysis of the tibia (maximum axial force 420% body weight [% bw]) [14], axial forces in sheep tibia were measured much lower (89% bw [11] and 110% bw [12]) These discrepancies might be explained with the quadruped gait. The objective of the present study was telemetric evaluation of in vivo axial forces, bending moments, and bending moment angles in the rabbit tibia with weight bearing in free physiological movement to prove our hypothesis that axial forces and bending moments in the mid-diaphysis of rabbit tibia differ from other experimental animals or indirectly calculated data

Objectives

Methods

Results

Discussion

Conclusion