Quantifying Massive Allograft Healing of the Canine Femur In Vivo and Ex Vivo: A Pilot Study
- 338 Downloads
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.
We thank our collaborative authors from the University of Rochester, Masahiko Takahata, MD, and Chao Xie, MD, for their assistance in the daily observations of the canine subjects and care for the animals during DCE-MRI and CB-CT; David Conover, MS, for his help running the CB-CT scanner; and Hani A. Awad, PhD, for help with the experimental design and data analyses. We also thank Synthes Inc for providing surgical equipment and implants.
- 11.Ito H, Koefoed M, Tiyapatanaputi P, Gromov K, Goater JJ, Carmouche J, Zhang X, Rubery PT, Rabinowitz J, Samulski RJ, Nakamura T, Soballe K, O’Keefe R J, Boyce BF, Schwarz EM. Remodeling of cortical bone allografts mediated by adherent rAAV-RANKL and VEGF gene therapy. Nat Med. 2005;11:291–297.PubMedCrossRefGoogle Scholar
- 13.Looney RJ, Boyd A, Totterman S, Seo GS, Tamez-Pena J, Campbell D, Novotny L, Olcott C, Martell J, Hayes FA, O’Keefe RJ, Schwarz EM. Volumetric computerized tomography as a measurement of periprosthetic acetabular osteolysis and its correlation with wear. Arthritis Res. 2002;4:59–63.PubMedCrossRefGoogle Scholar
- 31.Yazici C, Takahata M, Reynolds DG, Xie C, Samulski RJ, Samulski J, Beecham EJ, Gertzman AA, Spilker M, Zhang X, O’Keefe RJ, Awad HA, Schwarz EM. Self-complementary AAV2.5-BMP2-coated femoral allografts mediated superior bone healing versus live autografts in mice with equivalent biomechanics to unfractured femur. Mol Ther. 2011;19:1416–1425.PubMedCrossRefGoogle Scholar
- 32.Zabka AG, Pluhar GE, Edwards RB 3rd, Manley PA, Hayashi K, Heiner JP, Kalscheur VL, Seeherman HJ, Markel MD. Histomorphometric description of allograft bone remodeling and union in a canine segmental femoral defect model: a comparison of rhBMP-2, cancellous bone graft, and absorbable collagen sponge. J Orthop Res. 2001;19:318–327.PubMedCrossRefGoogle Scholar