Background and purpose: Hydroxyapatite (HA) coating stimulates the osseointegration of cementless orthopedic implants. Recently, locally released osteogenic growth factors have also been shown experimentally to stimulate osseointegration so that bone fills gaps around orthopedic implants. Here, we have compared the effect of local release of TGF-β1 and IGF-1 with that of hydroxyapatite coating on implant fixation. Method Weight-bearing implants with a 0.75-mm surrounding gap were inserted bilaterally in the knees of 10 dogs. Growth factors were incorporated in a biodegradable poly(D,L-lactide) coating on porous coated titanium implants. Plasma-sprayed HA implants served as controls. The dogs were killed at 4 weeks and the implants were evaluated by mechanical push-out test and by histomorphometry. Results: There was no difference in any of the mechanical parameters. Bone ongrowth was 3-fold higher for HA-coated implants (p < 0.001). For growth factor-coated implants, bone volume was 26% higher in the inner half of the gap and 28% higher in the outer half compared to HA (p < 0.03). Interpretation: The mechanical fixation of porous-coated titanium implants with local growth factor release is comparable to that of HA coating. While HA mainly stimulated bone ongrowth, local release of TGF-β1 and IGF-1 stimulated gap healing.
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The authors thank Anette Milton, Jane Pauli, and Feng Ya Mei for technical assistance. Niels Trolle Andersen of the Department of Biostatistics, University of Aarhus, provided invaluable help with statistics. The Interdisciplinary Research Group, Nanoscience and Biocompatibility, Danish Research Agency, provided financial support (grant no.2052-01-0049). The Danish Rheumatism Association, Kurt Bønnelycke og Hustru Grethe Bønnelyckes Fond, and the Max og Anna Friedmanns Legat til Sygdomsbekæmpelse also kindly supported the study.