Role of dynamic loading on mesenchymal stem cells and growth factors transport in bone fracture healing under locking plate fixation.

Abstract

Introduction When fracture healing is facilitated by flexible fixation like locking compression plates (LCP), the stiffness of fixation along with the mechanical loading of bone influences biological processes like cell migration. In this study, we investigate the effect of different LCP configuration, i.e. bone plate distance (BPD) and working length (WL) on mesenchymal stem cells (MSCs) and growth factors transport under dynamic loading.

Methods A plane symmetry 2D geometry was adopted for computation from a 3D model obtained from the CT scanning image of the human femur bone, and cyclic loading (150N @ 1Hz) similar to human foot loading pattern was applied. The fracture callus is considered as a poroelastic material and transport equations for MSCs and growth factors are based on the conservation of mass while fluid flow motion is derived from Darcy’s law.

Results Over the course of 5 hours, enhancement of MSC uptake in callus due to dynamic loading was highest in the most flexible fixation (C4-100). Similarly, osteogenic and chondrogenic growth factors were enhanced by around 140% and 300%, respectively.

Conclusion A physiologically relevant dynamic loading could enhance the transport of MSCs and growth factors into callus by 25% and growth factors by 300% respectively. For same LCP configuration, gap size of 3mm has higher enhancement over 1mm in cells and growth factors, suggesting that enhanced transport is gap size dependent.