Pediatric Orthopedic Trauma

Infl ammation describes the initial phase after a loss of integrity of the osseus structure. The haematoma formed due to ruptured blood vessels plays a central role. It fi lls the fracture gap, contains a lot of fi brin and infl ammatory mediators that attract mesenchymal cells. Certain proteins are responsible for the differentiation of mesenchymal cells into chondroblast, osteoblasts, and angioblasts, a process that closely resembles the stages of bone development. Callus formation takes place in the reparative phase. Initially, the hard callus is formed by periostal cells that directly differentiate into osteoblasts which lay down bone by intramembranous ossifi cation. In the centre of the fracture gap chondrocytes form the soft callus which serves as a scaffold for woven bone formed by endochondral ossifi cation. The hard and the soft callus together represent the so-called provisional callus that provides temporary stabilization. Rigid stability that is necessary for full physical activity occurs when lamellar bone is laid down along the lines of stress and replaces the provisional callus. This remodelling phase can last months, even years in certain osseus structures.