Modulation of the soft tissue reactions to percutaneous orthopaedic implants

To evaluate soft tissue reactions and biofilm formation on percutaneous external fixator screws coated with diamond-like carbon (DLC) and hydroxyapatite (HA) coatings on stainless-steel (SS) pins in an ovine loaded osteotomy model, an Orthofix external fixator was used to stabilize a 3-mm tibial midshaft osteotomy with six tapered pins inserted into the right tibia of 32 skeletally mature Friesland ewes. Animals were divided into four groups; SS, fully coated HA, DLC, and HA-coated threads. At 10 weeks, specimens were harvested and the pins were removed en bloc to examine the interfaces between the surface coatings and the tissues. Fully coated HA pins had a significantly higher percentage of dermal contact with the pin surface than HA-coated threads (p=0.028). The presence of a biofilm was evident on all pin surfaces except DLC-coated pins. Significantly greater numbers of bacteria were present on fully coated HA and plain stainless-steel pins compared with DLC. The surface of DLC-coated pins had a significantly lower number of bacterial colonies compared to SS (p=0.028) and fully coated HA pins (p=0.005). Fully coated HA pins have greater dermal attachment to the pin surface than the other pin coatings investigated. DLC-coated pins have the potential to prevent biofilm formation and bacterial colonization that may reduce infection and consequent pin loosening. An external fixator pin that is partially coated with HA to encourage bone and soft tissue integration and with DLC to reduce biofilm formation is advocated.