Retarded mineralization cascade in an experimental nonunion--a sequential polyfluorochrome labeling study in rats

Although the early phases of the healing seem to occur normally, the persistent rotational instability between the fracture fragments combined to periosteal manipulation at the fracture site cause a failure in the restoration process of bone; i.e. the bridging event of the fracture ends does not occur and the tissue in the interfragmentary area is not mineralized. A nonunion with a soft tissue connection between the fragments is formed without restoration of the biomechanical characteristics of the bone.

A nonunion model of the rat femur was employed to study the mineralization process of developing pseudoarthrosis using the sequential polychrome labeling and conventional histological hard tissue staining with Masson-Goldner trichrome method.

The same results of this study are in accordance with previous studies using the same nonunion model and suggest that if sufficient mechanical stability between the fracture fragments has not been achieved within optimal time period, the chondral phase of the callus is extended and the mineralization process of the hypertrophied chondrocytes is retarded and finally extinguished and the fracture gap is filled with non-mineralizing connective tissue.