title: A comparison of hydroxyapatite-coated, titanium-coated, and uncoated tapered external-fixation pins. An in vivo study in sheep.
abstract: Three types of surfaces for external fixation pins were compared. One hundred and eight stainless-steel tapered 5/6-millimeter pins were divided into three groups: thirty-six pins remained uncoated (Group A), thirty-six were plasma-sprayed with hydroxyapatite (Group B), and thirty-six were plasma-sprayed with titanium (Group C). The pins were implanted in the left tibia of eighteen sheep, with each sheep receiving six pins from the same group. A unilateral fixator then was assembled on the pins. The medial aspect of the mid-part of the tibial diaphysis was exposed, and a five-millimeter-long cylinder of bone was removed so that load would be borne by the bone-pin interfaces. Six weeks after the procedure, radiographs demonstrated rarefaction of twenty-nine pin tracks in Group A, fifteen in Group B, and thirty in Group C (p = 0.021 for Group A compared with Group B and p = 0.016 for Group B compared with Group C). The mean final insertion torque (and standard deviation) was 4360+/-1050 newton-millimeters in Group A, 3420+/-676 newton-millimeters in Group B, and 3740+/-643 newton-millimeters in Group C. With the numbers available, no significant differences could be detected among these values. The mean extraction torque was 253+/-175 newton-millimeters in Group A, 3360+/-1260 newton-millimeters in Group B, and 1720+/-1030 newton-millimeters in Group C (p = 0.002 for Group A compared with Group B, p = 0.017 for Group A compared with Group C, and p = 0.03 for Group B compared with Group C). The extraction torque was significantly lower than the corresponding insertion torque in both Group A (p < 0.001) and Group C (p = 0.003); no significant difference could be found, with the numbers available, in Group B (hydroxyapatite-coated pins). At sixty times magnification, direct contact was seen along a mean of 16+/-9 per cent of the bone-pin interface in Group A, 30+/-12 per cent of the interface in Group B, and 28+/-15 per cent of the interface in Group C (p = 0.042 for Group A compared with Group C). However, at 10,000 times magnification, direct bone-pin contact was found only in Group B.
authors.affiliation: Department of Orthopaedic Surgery, Bologna University, Rizzoli Orthopaedic Institute, Italy. a.moroni.ior@tizeta.it
authors.forename: A
authors.initials: A
authors.lastname: Moroni
authors.forename: S
authors.initials: S
authors.lastname: Toksvig-Larsen
authors.forename: M C
authors.initials: MC
authors.lastname: Maltarello
authors.forename: L
authors.initials: L
authors.lastname: Orienti
authors.forename: S
authors.initials: S
authors.lastname: Stea
authors.forename: S
authors.initials: S
authors.lastname: Giannini
mesh_terms: D000818:Animals; D001858:Bone Nails; D017886:Durapatite; D016267:External Fixators; D008855:Microscopy, Electron, Scanning; D011859:Radiography; D012756:Sheep; D013499:Surface Properties; D013977:Tibia / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D014025:Titanium
chemical_list: D017886:Durapatite; D014025:Titanium