Expression of matrix genes during incorporation of cancellous bone allografts and autografts.

The healing process of cylindrical metaphyseal bone defects filled with fresh autogeneic or frozen allogeneic cancellous bone grafts was studied using histology, biomechanical testing, and molecular biology. The results were compared with the healing pattern observed in nongrafted defects, where a strong initial expression of Type III collagen was followed by slowly starting expression of osteonectin and Type 1 collagen genes. Autogeneic or allogeneic cancellous bone grafts considerably increased the healing rate of the defects. The sequence of healing was similar with both types of grafts, but the maximal levels of Type III and Type I collagen messenger ribonucleic acids (mRNAs) were delayed by 1 week when allografts were used. Histologically, during the initial phase the grafts had an invasion of progenitor mesenchymal tissue within 2 weeks followed by intramembranous bone formation and by a gradual decline in Type I collagen expression. Osteonectin mRNA was present throughout the healing process, but no expression of Type II collagen was seen. Indentation testing showed no significant biomechanical differences between the autografts and allografts. Histology and molecular biology testing results revealed that the production of extracellular matrix starts slower in allogeneic cancellous bone grafts than in autografts, suggesting a basic difference in the initial host tissue response between autogeneic and allogeneic bone grafts.