The Effect of External Fixator Pin Geometry and Dynamic Loading on Bone Remodelling at the Pin-Bone Interface (PBI), in an In Vivo Sheep Tibia Model

Abstract

SummaryThe purpose of this study was to study the effects of pin design and dynamic loading on the biological response of bone at the pin-bone interface (PBI). An electro-pneumatic pin-loading device was used to mimic the forces that would be experienced by external fixator pins, during patient ambulation following repair of a fracture with external skeletal fixation. The remodelling response was assessed histologically with fluorescence microscopy of plasticembedded undecalcified pin-bone sections, and surface-stained histomorphometry.There were no significant differences between the AO Schanz and Howmedica Apex 5.0 mm diameter self-tapping pin designs when they were inserted in 4.5 mm diameter predrilled pilot holes. When pin type was controlled for, significant differences (p<0.05) existed between loaded and control groups as well as between entry (near) and exit (far) cortices. Less bone resorption was observed in the non-loaded group in comparison to the dynamically loaded group, and bone resorption in the near cortex consistently exceeded the amount of bone resorption in the far cortex for both treatment groups.The purpose of this study was to examine the effects of pin design and dynamic pin loading on the remodelling response of cortical bone at the pin-bone interface (PBI) of intact sheep tibiae. No significant differences were demonstrated between pin designs; however, significant differences (p<0.05) existed between loaded versus control pins, as well as between entry and exit cortices.