Connective tissue parameters in experimental nonunion

A previously developed experimental model for producing nonunions in rats was used to study the biochemical changes of connective tissue parameters in impaired fracture repair. The model is based on rotational instability between the fracture fragments. A mid-diaphyseal femoral osteotomy was performed on 30 male rats and fixed with a loose-fitting intramedullary nail. The rats were killed 1, 2, 3, 7, 9, and 12 weeks postoperatively, and the development of nonunions was verified with radiographs. The calluses were dissected free and set for biochemical analysis. The contents of nitrogen, hydroxyproline, calcium, and phosphorous, as well as the RNA/DNA ratio, were determined. It appeared that in the impaired fracture repair there is an extended matrix production phase continuing until 7 weeks postoperatively. Simultaneously, the number of callus cells increased, indicating an extended expression of the mitotic signals for callus cells. The net synthesis of collagen matrix seemed to be sufficient, but the mineral binding capacity of the newly synthetised collagen was impaired. Later, the cessation of chondrogenic and osteogenic activity could be observed with the formation of nonmineralized fibrous tissue between the fracture fragments.