Summary
The purpose of this study was to examine the effect of pin design and drill/pin cooling
on the biological response of bone in the near (entry) and far (exit) cortices of
mature intact sheep tibiae. Two pins with markedly different characteristics were
used; the AO Schanz screw, a traditional pyramidal tipped design, and the fluted,
tapered end Howmedica Apex pin. Our hypothesis was that cooling of hardware would
reduce thermal necrosis of bone at the pin-bone interface (PBI). When the effect of
pin design was controlled for, the cooled pins resulted in better pin bone interfaces
at the near cortex but not the far cortex. It is possible that the drill bits and
pins warmed significantly after traversing the more vascular bone marrow space, thus
the cooling effect was lost before drilling the far cortex. Secondly, the Howmedica
Apex pin resulted in more bone at the pin bone interface than the AO Schanz pin indicating
that the former’s more advanced design follows the pilot hole and creates threads
more accurately, resulting in a better pin-bone fit and less mechanical damage.
The purpose of this study was to examine the effects of pin design and drill/pin cooling
on the remodelling response of cortical bone at the pin-bone interface in an in vivo sheep tibia model. No significant differences were found between pin designs or between
pins that were implanted at 4° C and those that were inserted at 20° C. More bone
was retained at the near cortex pin-bone interface (PBI) than the far cortex PBI when
the pins were cooled, but the opposite was true when the pins were not cooled.
Keywords
External fixai or pin-bone interface - thermal damage - bone remodelling
