Estudio biomecánico del proceso de consolidación de fracturas con sistemas de fijación externa rígidos y elásticos

To study the differences between rigid and elastic external fixation,the authors have designed an external fixator, used at thetibia of the rabbit, which allows a rigid behaviour and with thepossibility of transformation in an elastic system. They have carriedout a theoretical study of the fixator by 'finite elements'method and an experimental study, biomechanical, morfologicaland 'in vivo' monitoritation of the callus of fracture.The theoretical study showed that the weights supported bythe fracture's callus depended on their elastic characteristics andnot on the immobilization method used (rigid or elastic).At the fracture callus of the rabbit tibias there were no differencesof resistance to the traction with either methods (rigid or elastic).There were also no histological differences in the evolution ofthe callus.The "in vivo" monitoritation through force measuranient showeda rapid increase in the rigidity of the callus between thesecond and third week.The overall interpretation of the results, both theoretical andexperimental, established the necessity of rigidity of t h e system ofexternal fixation in the initial estages of consolidation that garanticesa mechanical protection of the callus in that moment.The behaviour of this "rigid" system is praticaly identical tothat presented by "elastic" systems, when the callus acquires someelastic characteristics that permits it to support weights. Thisoccurs when more than 20 % of the total consolidation time of t hefracture has passed.

To study the differences between rigid and elastic external fixation,the authors have designed an external fixator, used at thetibia of the rabbit, which allows a rigid behaviour and with thepossibility of transformation in an elastic system. They have carriedout a theoretical study of the fixator by 'finite elements'method and an experimental study, biomechanical, morfologicaland 'in vivo' monitoritation of the callus of fracture.The theoretical study showed that the weights supported bythe fracture's callus depended on their elastic characteristics andnot on the immobilization method used (rigid or elastic).At the fracture callus of the rabbit tibias there were no differencesof resistance to the traction with either methods (rigid or elastic).There were also no histological differences in the evolution ofthe callus.The "in vivo" monitoritation through force measuranient showeda rapid increase in the rigidity of the callus between thesecond and third week.The overall interpretation of the results, both theoretical andexperimental, established the necessity of rigidity of t h e system ofexternal fixation in the initial estages of consolidation that garanticesa mechanical protection of the callus in that moment.The behaviour of this "rigid" system is praticaly identical tothat presented by "elastic" systems, when the callus acquires someelastic characteristics that permits it to support weights. Thisoccurs when more than 20 % of the total consolidation time of t hefracture has passed.