title: A method to determine the 3-D stiffness of fracture fixation devices and its application to predict inter-fragmentary movement.
abstract: Inter-fragmentary movement considerably influences the fracture healing process. Large shear movement delays while moderate axial movement stimulates the healing process. To be able to control the mechanical situation at a fracture site and to achieve optimal bony healing it is essential to understand the relationship between inter-fragmentary movement, bony loading and fixation stiffness. A 6 x 6 stiffness matrix is introduced which completely describes the linear relationship between the 6 inter-fragmentary movements and the resulting bony loading (3 forces and 3 moments). Further, it is illustrated that even in relatively stiff external fixateur constructs simple axial loading of the bony fragments leads to complex inter-fragmentary movement. When the 3-D stiffness description is multiplied by the load state in sheep tibiae, movements similar to those measured in vivo are calculated. The relationship between axial compression and medio-lateral or dorso-ventral shear varies depending on the mounting plane of the external fixateur. The authors conclude that a single value is not sufficient to describe the mechanical relationship between inter-fragmentary movement and bony loading. Only a complete description of fixation stiffness allows prediction of inter-fragmentary movement and differentiation between various configurations of fixation devices and their potential for mechanically promoting bony healing.
authors.affiliation: Department of Unfallchirurgische Forschung und Biomechanik, University of Ulm, Germany. duda@ukrv.de
authors.forename: G N
authors.initials: GN
authors.lastname: Duda
authors.forename: H
authors.initials: H
authors.lastname: Kirchner
authors.forename: H J
authors.initials: HJ
authors.lastname: Wilke
authors.forename: L
authors.initials: L
authors.lastname: Claes
mesh_terms: D000818:Animals; D004548:Elasticity; D004867:Equipment Design; D005544:Forecasting; D005592:Fracture Fixation / Q000295:instrumentation*; D017102:Fracture Healing / Q000502:physiology*; D008422:Materials Testing / Q000295:instrumentation; D008722:Methods; D009068:Movement; D009984:Orthopedic Fixation Devices; D012756:Sheep; D013978:Tibial Fractures / Q000503:physiopathology*