Summary
Destabilization is a concept of pursuing gradual staged disassembly of external skeletal
fixators (ESFs) intending to increase only axial loading of the fracture while controlling
non-axial loading. The purpose of this study was to determine how destabilization
alters loading at the fracture site. The destabilization of a Type III to a Type Ia
and Ib ESF was analyzed with the Finite Element Method (FEM) for five callus stages
(0%, 0.1%, 10%, 50%, 100% modulus of elasticity of intact bone) for axial compression,
torsion, and bending. Axial gap strain (A) comprising the linear displacement along
the longitudinal bone axis, the remaining degrees of gap strain (R) comprising all
other rotational and linear displacements and the R/A ratio were calculated. In the
presence of the callus stages 0% and 0.1%, the R/A ratio ranges between 0.1 and 0.3.
Destabilization increases A by two to18 fold and R by five to 41 fold. In the presence
of the callus stages 10%, 50% and 100%, the R/A ratio ranges between 1 and 3.2. Destabilization
increases A by 2% -15%, and R by 15% -176%. A decrease in the ESF stiffness correlates
with an increase of R, A and the R/A ratio. We proposed that the clinical benefits
of destabilization might be mechanically based on optimization of the R/A ratio and
not of axial strain.
Keywords
External skeletal fixators - FEM - destabilization - axial strain
