STABILIZATION OF AN INSERTED TRICALCIUM PHOSPHATE SPACER ENHANCES THEHEALING OF A SEGMENTAL TIBIAL DEFECT IN SHEEP

The effect of inserting a tricalcium phosphate (TCP) spacer stabilized by a rigid or non-rigid fixation technique on the healing of segmenta l tibial defects of critical size was established. The osteotomized ti biae, 11 with and 8 without TCP spacers, were fixed by an external cir cular device in 11 mature sheep and by plates in 8 mature sheep, respe ctively. Healing was evaluated roentgenographically 16 weeks after the operation. Compared with the defects without TCP spacers, enhanced st ability and healing were observed in the defects with TCP spacers unde r an identical external fixation. Furthermore, a significantly higher incidence of healing was obtained with plate fixation than with extern al device fixation in the TCP-implanted defects (P < 0.04). An abundan t bridging callus was roentgenograpically demonstrated in most of the healed defects, but none in the unhealed defects. The TCP spacer with its mechanical integrity enhances the stability of external fixation, and the stable immobilization provided by rigid fixation is essential for osteoconduction of an inserted TCP spacer in the healing of segmen tal diaphyseal defects in sheep.