title: Hydroxyapatite coated external fixation pins: an experimental study.
abstract: A sheep model was developed for the implantation of 84 bicylindrical stainless steel external fixation pins. One-half of the pins were coated with hydroxyapatite, and the rest remained uncoated. A set of 6 pins with the same coating was implanted in the lateral side of the left tibias of 14 sheep, the final insertion torque was measured, and a monolateral external fixator was assembled on the pins. The medial tibial middiaphysis then was exposed and a 5-mm resection osteotomy was done. Sheep were euthanized 6 weeks after surgery, radiographs were taken, and the initial extraction torque was measured on 4 pins from each sheep. Undecalcified sectioning and histologic and histomorphometric analyses were done on the remaining 2 pins. Radiographic pin tract rarefaction was significantly lower in the hydroxyapatite coated pins compared with the uncoated pins. Group average insertion torque was 960 +/- 959 Nmm in the hydroxyapatite coated pins and 709 +/- 585 Nmm in the uncoated pins. Group average initial extraction torque was 1485 +/- 1308 Nmm and 298 +/- 373 Nmm, respectively. Bone pin contact was 85.7% +/- 8.9% and 50.3% +/- 20.4%, respectively, in hydroxyapatite coated and uncoated pins. Bone between the threads was 95.6% +/- 5.7% and 80% +/- 8.7%, respectively, in hydroxyapatite coated and uncoated pins. Hydroxyapatite coating was effective for improving the bone-to-pin interface.
authors.affiliation: Third Department of Orthopaedic Surgery, Rizzoli Orthopaedic Institute, Bologna, Italy.
authors.forename: V L
authors.initials: VL
authors.lastname: Caja
authors.forename: A
authors.initials: A
authors.lastname: Moroni
mesh_terms: D000818:Animals; D001858:Bone Nails / Q000592:standards*; D004195:Disease Models, Animal; D004867:Equipment Design; D016267:External Fixators / Q000592:standards*; D005260:Female; D006882:Hydroxyapatites; D008422:Materials Testing; D011859:Radiography; D012756:Sheep; D013978:Tibial Fractures / Q000000981:diagnostic imaging / Q000473:pathology / Q000628:therapy*
chemical_list: D006882:Hydroxyapatites