An ovine model to evaluate the biologic properties of impacted morselized bone graft substitutes

The objectives of this study were to develop and evaluate a bone-defect model to study the biologic behavior of biomaterials being considered for impaction grafting in revision hip arthroplasty. A miniature impactor was designed to produce pellets of aggregates at a standard compactive effort. In Phase 1, 22 sheep underwent implantation of pellets into six metaphyseal defects in both rear limbs. In Phase 2, eight sheep underwent surgical implantation of four pellets in metaphyseal defects. Defects were sealed with polymethylmethacrylate in both phases. Healing of the defects was evaluated at 7 weeks (Phase 1, n = 11) and 14 weeks (n =19) with computed tomography, histology, and histomorphometry. Complications in Phase 1 included four femoral fractures and migration of cement seals (18/102 defects). No complications occurred in Phase 2. Whereas no difference was found between left and right limbs, osteogenesis and incorporation of biomaterials varied among implantation sites. For comparison of grafting materials, treatment site allocations were randomized according to a Latin square design. This model allows evaluation of several impacted aggregates (including large particles) in the same animal. It is particularly suitable for analyzing the biologic properties of grafting materials prior to evaluation under loading conditions.