title: 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.
abstract: 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.
authors.affiliation: Department of Trauma and Orthopedic Surgery, University of Witten/Herdecke, Faculty of Health - School of Medicine, Cologne Merheim Medical Center, Ostmerheimerstr, 200, 51109 Cologne, Germany. t.tjardes@bdc.de.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Tjardes
authors.forename: Michael
authors.initials: M
authors.lastname: Roland
authors.forename: Robin
authors.initials: R
authors.lastname: Otchwemah
authors.forename: Tim
authors.initials: T
authors.lastname: Dahmen
authors.forename: Stefan
authors.initials: S
authors.lastname: Diebels
authors.forename: Bertil
authors.initials: B
authors.lastname: Bouillon
mesh_terms: D001860:Bone Plates / Q000592:standards; D020342:Finite Element Analysis / Q000592:standards; D005593:Fracture Fixation, Internal / Q000379:methods* / Q000592:standards; D006801:Humans; D013314:Stress, Mechanical; D013978:Tibial Fractures / Q000473:pathology / Q000601:surgery*; D014025:Titanium / Q000008:administration & dosage
chemical_list: D014025:Titanium