A Method to Determine the 3-D Stiffness of Fracture Fixation Devices and Its Application to Predict Inter-Fragmentary Movement

J Biomech. 1998 Mar;31(3):247-52. doi: 10.1016/s0021-9290(97)00115-2.

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.

MeSH terms

  • Animals
  • Elasticity
  • Equipment Design
  • Forecasting
  • Fracture Fixation / instrumentation*
  • Fracture Healing / physiology*
  • Materials Testing / instrumentation
  • Methods
  • Movement*
  • Orthopedic Fixation Devices*
  • Sheep
  • Tibial Fractures / physiopathology*