Quantifying Massive Allograft Healing of the Canine Femur In Vivo and Ex Vivo: A Pilot Study
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- Santoni, B.G., Ehrhart, N., Betancourt-Benitez, R. et al. Clin Orthop Relat Res (2012) 470: 2478. doi:10.1007/s11999-012-2349-9
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Allograft integration in segmental osseous defects is unpredictable. Imaging techniques have not been applied to investigate angiogenesis and bone formation during allograft healing in a large-animal model.
We used dynamic contrast-enhanced (DCE)-MRI and cone beam (CB)-CT to quantify vascularity and bone volume in a canine femoral allograft model and determined their relationship with biomechanical testing and histomorphometry.
Femoral ostectomy was performed in three dogs and reconstructed with a 5-cm allograft and compression plate. At 0.5, 3, and 6 months, we performed DCE-MRI to quantify vascular permeability (Ktrans) and perfused fraction and CB-CT to quantify bone volume. We also performed posteuthanasia torsional testing and dynamic histomorphometry of the grafted and nonoperated femurs.
DCE-MRI confirmed the avascular nature of allograft healing (perfused fraction, 2.08%–3.25%). CB-CT demonstrated new bone formation at 3 months (26.2, 3.7, and 2.2 cm3) at the graft-host junctions, which remodeled down at 6 months (14.0, 2.2, and 2.0 cm3). The increased bone volume in one subject was confirmed with elevated Ktrans (0.22) at 3 months. CB-CT-identified remodeled bone at 6 months was corroborated by histomorphometry. Allografted femurs recovered only 40% of their strength at 6 months.
CB-CT and DCE-MRI can discriminate differences in angiogenesis and bone formation in the canine allograft model, which has potential to detect a small (32%) drug or device effect on biomechanical healing with only five animals per group.
These radiographic tools may have the potential to assess adjuvant effects on vascular invasion and new bone formation after segmental allograft transplantation.