The pin/bone-interface in external fixators - a biomechanical and biological analysis in a sheep model

The pin/bone-interface is the most critical point of the external fixator and determines the success of the whole treatment. To minimize the risk of complications during fracture healing, a stable integration of pins in the bone is required initially, as well as permanently. The hypothesis of this study was that the incidence of pin loosening and pin infection would increase, while the general stability of the pin/bone-interface would decrease with ongoing implantation time. Therefore, 24 sheep received a tibial osteotomy stabilized by an external fixator. The pin/bone-interface was analyzed radiologically, biomechanically, microbiologically and histologically after 3, 6, and 9 weeks. Contrary to our hypothesis, this study showed that the biomechanical pin anchorage during implantation time (weeks 3 to 9) did not alter. This effect may be attributable to an increasing remodelling found in the callus and cortex around the pins and was promoted by a strict pin care routine and consequently a lower infection rate.