[Long-term radiologic evolution of coral implanted in cancellous bone of the lower limb. Madreporic coral versus coral hydroxyapatite].

Purpose: The study aimed to compare two successive series of procedure using first pieces of natural madreporic coral, then coralline hydroxyapatite in traumatology. The goal of this work was to evaluate long term radiological features of absorption and influencing factors.
Material: Within six years, 65 pieces were used; only impaction articular fracture on the lateral tibial plateau (31) and calcaneum fractures (23) were included 21 cases completed inclusion criteria. As there were 3 secondary infections, 18 had therefore, an aseptic evolution and were included in this series.
Methods: Absorption was evaluated in five degrees according to the volume of the remaining piece on X-rays. We also took into consideration the position of the pieces and the amount of surfaces in contact with cancellous bone.
Results: Among the 18 pieces followed up for more than 19 months (average 40), there were 4 sequestrations (1 tibia, 3 calcaneum), all were natural madreporic coral, the others presented osteointegration. Only natural madreporic coral pieces were absorbed, but never completely and the absorption was slow (3 to 7 years) and never complete. A radiolucent line was present in 7 out of 10 pieces of madreporic coral and none around coralline hydroxyapatite. Three developed favorably. Four were sequestred. Number of surfaces in contact with cancellous bone was correlated with osteointegration.
Discussion: The calcium carbonate which makes up the natural madreporic coral pieces is the site of destruction by osteoclasts. The radiolucent line is the specific witness of this biochemical activity. The radiolucent line proceeds sequestrations. No substitute of coralline hydroxyapatite has presented the same sign of peripheral absorption or sequestration. Coralline hydroxyapatite could be the correct coralline material to fill cancellous defect after elevation of an articular depression. In every case, the piece of coral must be fitted in contact with the cancellous bone in the depth of the bone. Conditions of osteoconduction of madreporic coral must be reconsidered. The degree and speed of peripheral absorption must be controlled before weight bearing is allowed.