Publikation
Less than full circumferential fusion of a tibial nonunion is sufficient to achieve mechanically valid fusion - Proof of concept using a finite element modeling approach
Thorsten Tjardes; Michael Roland; Robin Otchwemah; Tim Dahmen; Stefan Diebels; Bertil Bouillon
In: Catia Cornacchia (Hrsg.). BMC Musculoskeletal Disorders, Vol. 15, No. 1, Pages 1-7, BioMed Central, 2014.
Zusammenfassung
Background: Although minimally invasive approaches are widely used in many areas of orthopedic surgery
nonunion therapy remains a domain of open surgery. Some attempts have been made to introduce minimally
invasive procedures into nonunion therapy. However, these proof of concept studies showed fusion rates
comparable to open approaches never gaining wider acceptance in the clinical community. We hypothesize that
knowledge of mechanically relevant regions of a nonunion might reduce the complexity of percutaneous
procedures, especially in complex fracture patterns, and further reduce the amount of cancellous bone that needs
to be transplanted. The aim of this investigation is to provide a proof of concept concerning the hypothesis that
mechanically stable fusion of a nonunion can be achieved with less than full circumferential fusion.
Methods: CT data of an artificial tibia with a complex fracture pattern and anatomical LCP are converted into a
finite element mesh. The nonunion area is segmented. The finite element mesh is assigned mechanical properties
according to data from the literature. An optimization algorithm is developed that reduces the number of voxels in
the non union area until the scaled von Mises stress in the implant reaches 20% of the maximum stress in the
implant/bone system that occurs with no fusion in the nonunion area at all.
Results: After six iterations of the optimization algorithm the number of voxels in the nonunion area is reduced by
96.4%, i.e. only 3.6% of voxels in the non union area are relevant for load transfer such that the von Mises stress in
the implant/bone system does not exceed 20% of the maximal scaled von Mises stress occurring in the system
with no fusion in the non union area at all.
Conclusions: The hypothesis that less than full circumferential fusion is necessary for mechanical stability of a
nonunion is confirmed. As the model provides only qualitative information the observed reduction of fusion area
may not be taken literally but needs to be calibrated in future experiments. However this proof of concept provides
the mechanical foundation for further development of minimally invasive approaches to delayed union and
nonunion therapy.