EXCHANGE OF ILIZAROV EXTERNAL FIXATON BY INTRAMEDULLARY NAIL, DURING CALLUS CONSOLIDATION PHASE OF LIMB LENGTHENING. AN EXPERIMENTAL SHEEP MODEL

Abstract

We evaluate the effectiveness of external fixation exchange by intramedullary nailing during consolidation phase following callus distraction phase. In 12 skeletally mature female sheep, equally divided in two groups (group A and group B), we performed tibial shaft osteotomy and 2cm gradually callus distraction using Ilizarov external fixator in a 0.5mm/12h rate. In group A, immediately after lengthening completion, Ilizarov fixator was removed, and static unreamed intramedullary nail was inserted under fluoroscopic guidance. In group B (control group), Ilizarov frame remained (according to the usual technique) during consolidation phase. Callus maturity was studied in both groups, in specific time intervals, with plain x-rays, ultrasonograms, triplex and digital subscription angiograms. All animals were sacrificed 70 days after osteotomy and bone specimens including callus, were evaluated with MRI, DEXA and histopathologic examination.

In group A, all animals successfully tolerated intramedullary nailing, keeping limp alignment. All but one formatted a mature callus and kept callus length before being sacrificed. One sheep had a delayed formation of the callus and 0.5cm loss of callus length, because of failed insertion of distal locking screw in the nail. In group B, four of six formatted mature callus, two had axis disorder, three superficial pin-track infections and one deep infection in the same time.

We conclude that replacement of Ilizarov device by static unreamed intramedullary nail during callus consolidation phase decreases the total duration of external fixation, limits articular stiffness, pin-track infections and axial deformities, and provides protection against refracture. Our results suggest that there is no considerable difference between callus formations in the two groups.