The implantation of demineralized fracture matrix yields more new bone formation than does intact matrix.

The inductive capacity of demineralized/lyophilized bone matrix prepared from fractured tibia ends in rats at different intervals after fracture was compared with matrix from the opposite, intact tibia. Fracture matrix and normal matrix cut in longitudinal strips were implanted in the gluteal muscles of 47 rats and were harvested after 15, 30, and 50 days. Staining was performed with hematoxylin-eosin, toluidine blue, and by monoclonal antibodies against Ia-antigen and collagen II. In comparison to the normal matrix, the fracture matrix brought about a more rapid bone formation counted as mineralization after 30 days and formation of ossicles after 30 and 50 days. Matrix from eight-day-old fracture was the most potent inductor compared to matrix from the other post-fracture intervals (one, five, and 11 days). Typical for the responding cells surrounding the implanted matrix was the abundant occurrence of cells carrying Ia-antigen. The cells penetrating the matrix formed pseudopods and could therefore be characterized as dendritic cells. The higher inductive capacity of fracture matrix might have some importance for the formation of the inductive enchondral callus in normal fracture healing.