The Journal of Bone and Joint Surgery 80:547-54 (1998)
© 1998 The Journal of Bone and Joint Surgery, Inc.
A Comparison of Hydroxyapatite-Coated, Titanium-Coated, and Uncoated Tapered External-Fixation Pins. An in Vivo Study in Sheep*
ANTONIO MORONI, M.D. ,
SOREN TOKSVIG-LARSEN, M.D. ,
MARIA CRISTINA MALTARELLO, B.SC.,
LUCA ORIENTI, M.D.,
SUSANNA STEA, B.SC. and
SANDRO GIANNINI, M.D., BOLOGNA, ITALY
Investigation performed at the Department of Orthopaedic Surgery, Bologna University, Rizzoli Orthopaedic Institute, Bologna
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.
CLINICAL RELEVANCE: The better fixation and greater interface strength of the hydroxyapatite-coated tapered pins should lead to a substantial decrease in the frequency of loosening and infection and consequently to a remarkable improvement in the clinical results of external fixation.
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