Enhancement of the Bone External Fixation Pin Interface: a Biomechanical and Morphological In Vivo Experimental Study

ABSTRACT Eightyfour bicylindrical stainless steel external fixation pins were used. Half of the pins were coated with hydroxyapatite (HA). Six pins of the same type (HA coated or uncoated) were implanted monolaterally in the left tibiae of fourteen sheep, and a monolateral external fixator was assembled on the pins. Then the medial tibial mid-diaphysis was exposed and a bone cylinder five mm long was removed. Six weeks after surgery sheep were euthanized. Considering all the pins, independently from their position, mean extraction torque was 1485±1308 Nmm in the HA coated pins and 298±373 Nmm in the uncoated (p=0.0001). Histology showed extensive bony coverage of the HA coated pins, on the contrary severe fibrous tissue encapsulation was observed in the uncoated pins. The percentage of bone implant contact was 85.7±8.9 and 43.1±26.6 respectively in the HA coated and uncoated pins (p