BIOMECHANICAL ANALYSIS OF CANINE BONE LENGTHENED BY THE CALLOTASIS METHOD

The mechanical integrity of tibial bone treated by distraction osteoge nesis (callotasis) using an Orthofix external fixator was evaluated in a group of 6 dogs. Diaphyseal corticotomies were performed on Day 0. Distraction was begun on Day 8, at a rate of 0.33 mm every 8 hours. On Day 34, the Orthofix frame was locked. On Day 56, the frames were rem oved and the dogs were euthanized. Radiographs were taken weekly to as sess regenerate bone formation and extent of tibial bone lengthening, which averaged 12 mm (range, 5-20 mm). One dog showed incomplete bony union that was attributed to pin loosening. Torsional testing of lengt hened and contralateral control tibiae resulted in spiral diaphyseal f ractures. Five of 6 lengthened tibiae bones fractured within the diaph ysis, but outside the regenerate area, suggesting that the strength of the lengthened segment exceeded that of the original diaphysis which was exposed to stress shielding by the external fixator. These observa tions have led to a method to test and evaluate lengthened bone at the time of frame removal and to monitor the effectiveness of this type o f technique.