Aims: To evaluate the effectiveness of external fixation exchange by intramedullary nailing during consolidation phase following callus distraction phase. Methods: In 12 skeletally mature female sheep, equally divided in two groups (group A and group B), we performed tibial shaft osteotomy and 2cm gradual callus distraction using Ilizarov external fixator in a 0,5mm/12h rate. In group A, Ilizarov fixator was removed immediately after lengthening completion, and static unreamed intramedullary nail was inserted. In group B, Ilizarov device remained during consolidation phase. Formatted callus was studied, with radiographs, ultrasonograms, and triplex. All animals were sacrificed 70 days after osteotomy and bone specimens, were evaluated by DEXA and histopathologic examination. Results: In group A, all animals successfully tolerated intramedullary nailing and limb alignment was attained. All but one formatted mature callus and had started the remodeling phase retaining callus length, before being sacrificed. One animal had delayed callus maturation and 0,5cm loss of callus length, because of failed insertion of distal locking screw in the nail. In group B, all formatted mature callus too, but 2 had serious axis disorder, 3 persistent superficial pin-track infections and 1 deep infection in the same time. Conclusions: Replacement of Ilizarov device by static unreamed intramedullary nail during callus consolidation phase decreases the total duration of external fixation, limits joint stiffness, pin-track infections and axial deformities, and provides protection against refracture. Our results suggest that there is no considerable difference between callus maturation in the two groups.