Studies on the External Fixator Pin-Bone Interface: The Effect of Pin Design and Pin Cooling in an In Vivo Sheep Tibia Model

Abstract

SummaryThe 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.

In vitro comparison of two centrally threaded, positive-profile transfixation pin designs for use in third metacarpal bones in horses

“…15 By creating threads in a different, additional step, the surgery time may increase but clearance of bone debris in the present study seemed to be easier with the 2 long flutes in the NTTP tap. This phenomenon has been also noticed after inserting precooled pins into sheep tibiae, in which precooling of the pins has a positive effect at the cis cortex but the precooling effect is lost during insertion and at the trans cortex.…”

“…5,15,16 The threshold temperature for bone necrosis is believed to be 56°C because alkaline phosphatase denatures rapidly when exposed to this temperature. 5,15,16 The threshold temperature for bone necrosis is believed to be 56°C because alkaline phosphatase denatures rapidly when exposed to this temperature.…”

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

“…Since creating pilot holes of 4.25 mm diameter was not technically practical, both pin types were inserted into 4.5 mm diameter pilot holes for both treatment groups. This larger pilot hole made this experiment slightly different than our preceding study (24) because drilling a pilot hole greater than the core diameter resulted in a 0.25 mm gap that required some ingrowth of bone in all cases.…”

Management of tibial fractures with Orthofix axial external skeletal fixator in 15 dogs

“…The selection of screws or pins hasa n importanti nfluenceo nt he fixator's dy- namics andb iomechanics, pin track infection,pin loosening andfracture healing (33,35,44). We used Schanzscrewsinexternal skeletal fixation without anybreaksorcorrosion in screws and ring sequester formation in anyofthe cases.…”