COMPARISON OF DEMINERALIZED ALLOGENEIC BONE-MATRIX GRAFTING (THE URIST PROCEDURE) AND THE ILIZAROV PROCEDURE IN LARGE DIAPHYSEAL DEFECTS INSHEEP

The bone inductive capability of the Urist and Ilizarov procedures was compared in the repair of large diaphyseal defects in sheep. In 30 an imals, a 4 cm segmental defect was created in the middle portion of th e right femur and was stabilized with an external fixator. The sheep w ere divided into four groups according to the type of reconstruction o f the defect. In group 1, a demineralized allogeneic bone matrix (DABM ) cylinder was used; in group 2, DABM chips; and in group 3, gradual t ransport of a piece of bone detached from the proximal femoral fragmen t was used to fill the defect. Group 4 served as a control (the defect was left empty). New bone formation was assessed by serial radiograph s until the time of death at 2 or 4 months. Postmortem specimens were analyzed with respect to bone mineral content, uptake of isotopes (Ca- 45 and H-3-proline), and histology. The first signs of new bone format ion were radiographically evident at 4 weeks. In the two groups in whi ch reconstruction involved DABM (Urist procedures), new bone failed to form in eight of the 13 animals. Full bridging of the defect was obse rved at 8 weeks in one animal with a DABM cylinder and two with DABM c hips. No decisive difference in bone yield could be demonstrated betwe en the two Urist procedures. In the group treated with the Ilizarov pr ocedure, new bone formation consistently occurred at a high rate; full bridging of the defect was observed in seven of the eight animals. Bo ne mineral scanning and histologic analysis essentially confirmed the radiographic results. Uptake of isotopes was selectively analyzed in t wo sheep from each experimental group in which new bone formation was exhibited in the defect; new bone formation was increased compared wit h that in the contralateral femur but was equal among the three experi mental groups. Our study shows that gradual transport of a detached pi ece of autogeneic bone (Ilizarov procedure) is more effective than imp lantation of DABM (Urist procedure) in eliciting new bone formation in large diaphyseal defects in sheep. The variable bone induction by DAB M may be explained by differences in host immune responses to the impl ants.